• •■■■ \ 
I ■'-..- ij 







DENTAL METALLURGY 



FOR THE USE OF DENTAL STUDENTS 
AND PRACTITIONERS 



BY 

EWING PAUL BRADY, D.D.S. 

PROFESSOR OF CHEMISTRY, PHYSICS, METALLURGY, MATERIA MEDICA, THERA- 
PEUTICS AND SPECIAL PATHOLOGY, WASHINGTON UNIVERSITY 
DENTAL SCHOOL, ST. LOUIS, MISSOURI 



ITUustratefc wltb 62 Bnstavings 




LEA & FEBIGER 

PHILADELPHIA AND NEW YORK 
1917 



.31 



Copyright 

LEA & FEBIGER 

1917 



rt 



j*t 



JUN 15 1317 

Od A 462981 

1 



AS A TOKEN 

OF 
RESPECT AND APPRECIATION 

I WISH TO DEDICATE THIS TREATISE TO ONE WHOM I CONSIDER 
A PAST MASTER IN THE ART OF WORKING METALS 

WALTER M. BARTLETT, D.D.S. 



PREFACE. 



In this manual on the subject of dental metallurgy I have 
endeavored to emphasize those properties of the various 
metallic elements which are of particular interest to the 
dentist. 

As in every other science, there are branches which border 
on kindred sciences. Such operations as involve prosthesis 
are treated only in such detail as to emphasize the metal- 
lurgical principle involved. 

The chemical properties of the metals are dealt with 
very superficially, as this knowledge should have been 
acquired by the student before any attempt is made to 
study metallurgy. 

The chemical test for the metals, both in the dry and wet 
way, is placed in the back of the book. The object of this is 
twofold : in the first place it tends to condense the chapters 
on the individual metals, and secondly, the theme of analysis 
may be used in the study of qualitative analysis, and being 
condensed in one chapter is in more convenient form. 

The course in metallurgy, as I have been conducting it for 
a number of years, is given at the same time as the course 
on qualitative analysis. The advantage of such an arrange- 
ment is that the chemical properties of the metals are 
thoroughly studied in conjunction with metallurgy, in which 
the physical properties are of the greatest importance. 



vi PREFACE 

In the preparation of this volume I have made frequent 
references to the following valuable works on Metallurgy : 
Fenchel, Schnabel, and Essig and Koenig; on Chemistry: 
Oswald, Newth, Smith, and Remsen; Qualitative Analysis: 
Prescott and Johnson; Mineralogy: Moses and Parson, and 
Dana; Prosthetic Dentistry: Prothero; Assaying: Brown; 
Physics: Ganot; and the various scientific journals. 

I wish to express my appreciation to the following for their 
kindness in allowing me the privilege of using their illustra- 
tions: Central Scientific Co., E. H. Sargent & Co., Chicago; 
F. L. Schmidt & Co., New York City, and the Bureau of 
Mines, State of Colorado. 

E. P. B. 

St. Louis, 1917. 



CONTENTS, 



CHAPTER I. 
Metallurgy 17 

CHAPTER II. 
Metals 20 

CHAPTER III. 
Properties of the Metals 28 

CHAPTER IV. 
Alloys . 64 

CHAPTER V. 
Metallurgical Apparatus 77 

CHAPTER VI. 

Combination of Metals with the Non-metallic Elements 106 

CHAPTER VII. 
Lead 115 

CHAPTER VIII. 
Mercury 122 



Vlll 



CONTENTS 



CHAPTER IX. 



Silver 



Bismuth . 


CHAPTER X. 


Copper . 


CHAPTER XI. 


Cadmium 




Antimony . 


CHAPTER XIII. 


Tin . . 




Gold . . 


CHAPTER XV. 






CHAPTER XVII. 
Osmium, Iridium, P ALLADIUM; r„ 0DIUM) and Rctheniu 



Iron 



CHAPTER XVIII. 



CHAPTER XIX. 



Aluminum 



128 



143 



147 



155 



157 



161 



168 



199 



m . 211 



217 



235 



CONTENTS ix 

CHAPTER XX. 
Zinc 244 

CHAPTER XXI. 
Nickel . 254 

CHAPTER XXII. 
Tantalum. Tungsten , 258 

CHAPTER XXIII. 
Alkali and Alkali Earth Metals 263 

CHAPTER XXIV. 
Amalgams 270 

CHAPTER XXV. 
Methods of Dry Analysis 291 

CHAPTER XXVI. 
Wet Method of Analysis 298 

CHAPTER XXVII. 
Electrometallurgy 319 



DENTAL METALLURGY. 



CHAPTER I. 
METALLURGY. 

Historical. — The history of prehistoric ages depends upon 
relics for the study of the people living in the remote past. 
Depending upon the nature of these relics, it is possible to 
determine the state of civilization, habits and also peculiar- 
ities of the race under consideration. The lower savages of 
the present day correspond to the oldest traces of man. In 
order to leave traces, it was necessary for primitive man 
to make something, not subject to quick decay or easily 
destroyed. 

The age known as the " paleolythic" or "old stone age" is 
designated as that period in which man had advanced to that 
degree, which enabled him to work rocks into some useful 
form so as to serve in his daily life. Arrow-heads and various 
other flint implements, in their crudest form, are among the 
relics found corresponding to this age. The "neolythic," 
"new stone age," following this era, shows culture has 
advanced, and the stone implements in this period assume 
a higher degree of workmanship. 

The "neolythic" period varied in length of time in different 
localities; however, long ages must have passed before 
metals were made use of by mankind. Copper in its native 
state (too soft to be of material value to primitive man) , 
when hardened by the admixture of tin, forming bronze, was 
brought into use later. That this occurred in countries 
beyond the Mediterranean, before any people in Europe 
found the- metals secreted in their ores, appears to be more 
2 



18 METALLURGY 

than probable, and formerly it was assumed that the use of 
copper and bronze, followed later by the use of iron, came into 
Europe from the East. Now there is a growing opinion that 
primitive metallurgy in some parts of Europe was an art 
independently acquired. 1 The more advanced of the native 
races were acquainted with copper and bronze, tin, lead, 
gold, and silver. 

Sacred history teaches us that the metals were made use of 
at a very early age. One of Adam's grandsons was a worker 
in metals and frequent mention of gold, silver, bronze, etc., 
is made in the Bible. 

The development of chemical science has been divided 
into several stages, and as the early history of metallurgy 
is identical with that of chemistry, it may be permissible to 
quote the history of the two sciences as if they were one and 
the same. 

1. Ignorant Observation. — In this period experimentation 
was carried on in a haphazard manner, as no set laws had 
been formulated. The observer was simply following, as we 
may say, his own initiative. Rarely were records kept, and 
humanity or science was rarely benefited as the result of 
the efforts expended. 

2. Isolated Observation. — This period is so called because 
the investigators guarded very zealously their efforts: and, 
as a rule, worked in hidden places, and science was not 
benefited, due to the fact that there was no cooperation 
between the investigators of this period. 

Alchemy, with its prime object to find the philosopher's 
stone, may be classed in this period; and one may indeed 
excuse this set of men, when we consider the object of their 
endeavors was to find a substance which would change base 
metals into gold or silver. Their laboratories were sacred 
to them, no one was permitted to view their operations; 
mystic signs were used, and their favorite deity called upon 
to assist in their work. Up to this period the chief impetus 
to the development of chemistry was through the metallic 

1 Larned. 



TRUE SCIENTIFIC INVESTIGATION 19 

elements, and without a doubt this period may be considered 
the forerunner of the development of our present-day science 
of metallurgy. 

The phylogiston theory was the common belief of the 
alchemists; according to this theory a substance under- 
going rapid oxidation or combustion burned, losing phylo- 
giston. Combustible substances possessed phylogiston, non- 
combustible substances did not. This peculiar substance 
when combined with other substances made them weigh less, 
after burning, which was described as the act of a substance 
losing its phylogiston, the calx or ash resulting weighed more 
or possessed the original weight of the substance devoid of 
phylogiston. 

The elements were four, namely, earth, warm and moist; 
water, cold and moist; air, cold and dry; fire, hot and dry. 
With these four elements and the phylogiston theory, attempts 
were made to explain the various phenomena that were 
met with. 

3. True Scientific Investigation. — We may date this period 
with the introduction of the chemical balance by Lavoisier 
and the thorough understanding of the chemical phenomenon 
of oxidation about the year 1776. From this time we have 
the setting aside of the older theories such as have been 
mentioned, and the introduction by degrees of our present- 
day views upon the science of chemistry. 

One factor which has done more to further the progress of 
science than any other fact which may be brought to bear 
is that of cooperation of the investigators. By the combined 
efforts and setting of professional narrow-mindedness we 
have all gained knowledge from one another. 

It may be readily seen by reviewing the past that metal- 
lurgy has played its part in the rise of mankind from the 
primitive. As industry increased the needs for metals and 
alloys has increased correspondingly, and one has only to 
look to our own profession to see that at the present time 
there is a crying need for advancement and research investi- 
gation to provide for emergencies which have developed in 
the metallurgical side of dentistry. 



CHAPTER II. 
METALS. 

Metallurgy is a very extensive science and, like others, 
must depend upon its kindred sciences for its development. 
Geology, mineralogy, physics and chemistry, all have a 
direct bearing upon this science. A knowledge of chemistry 
and physics is absolutely necessary for the proper under- 
standing of metallurgy. 

Metallurgy may be defined as the science which treats of 
the physical and chemical properties, mode of occurrence, 
reduction from their ores, and application to useful purposes 
of the metallic elements. 

Chemistry teaches us that the universe is made up of 
matter and energy. Matter being composed of simple sub- 
stances called elements, and also a combination of these 
elements known as chemical compounds. The number of 
elements is constantly subject to change, and at the present 
time there are about eighty substances classed as elements. 
These are again divided into metals and non-metals. The 
names of the metallic elements and their principal valency 
so far known with certainty are as follows: 

International Atomic Weights. = 16. 1913. 
Symbol. 

Aluminum Al 

Antimony Sb 

Arsenic 1 As 

Barium Ba 

Bismuth Bi 

Cadmium . Cd 

Caesium Cs 

Calcium Ca 

Cerium Ce 

1 Metalloid. 



Valency. 


At, Wt. 


Ill 


27.1 


III or V 


120.2 


III or V 


74.96 


II 


137.37 


III or V 


208 . 


II 


112.4 


I 


132. SI 


II 


40.07 


III or IV 


140.25 



METALS 



21 



International Atomic Weights. 

Symbol. 

Chromium Cr 

Cobalt Co 

Copper Cu 

Erbium Er 

Gadelinium Gd 

Gallium Ga 

Germanium Ge 

Gold Au 

Indium In 

Iridium Ir 

Iron Fe 

Lanthanum La 

Lead Pb 

Lithium Li 

Magnesium Mg 

Manganese Mn 

Mercury Hg 

Molybdenum Mo 

Nickel Ni 

Niobium \ Nb 

Osmium Os 

Palladium Pd 

Platinum Pt 

Potassium - K 

Radium Ra 

Rhodium Rh 

Rubidium Rb 

Ruthenium Ru 

Samarium Sm 

Scandium Sc 

Selenium 1 Se 

Silver Ag 

Sodium Na 

Strontium Sr 

Tantalum Ta 

Tellurium Te 

Terbium Tr 

Thallium Tl 

Thorium Th 

Tin Sn 

Titanium Ti 

Tungsten W 

Uranium U 

Vanadium V 

Ytterbium Yb 

Yttrium Y 

Zinc Zn 

Zirconium Zr 



= 16. 1913.— (Continued.) 



II, 



Valency, 
II or 
II or 
I or 
III 
III 
III 
II or 
I or 
III 
III or 
II or 
III 
II or 
I 

II 
II, III or 
I or 

II, III, IV or 

II or 

III or 
II or 
II or 
II or 
I 
II 

III 

I 

II, III or 

III 

III 
II or 
I 
I 
II 
V 
II or 

III 
I or 

III or 
II or 

IV 
II, IV, V or 

III, IV, V or 

II or 
III 
III 

II 
IV 



III 
III 
II 



IV 
III 

IV 
III 

IV 



IV 

II 

V 

III 

IV 
IV 
IV 
IV 



IV 



IV 



VI 

III 

IV 
IV 

VI 

VIII 

IV 



At. Wt. 
52.0 
58.97 
63.57 
167.7 
157.3 
69.9 
72.5 
197.2 
114.8 
193.1 
55.84 
139.0 
207.1 
6.94 
24.32 
54.93 
200.6 
96.0 
58.68 
94.0 
190.9 
106.7 
195.2 
39.1 
226.4 
102.9 
85.45 
101.7 
150.4 
44.1 
79.2 
107.88 
23.0 
87.63 
181.5 
127.5 
159.2 
204.0 
232.4 
119.0 
48.1 
184.0 
237.0 
51.0 
172.0 
89.0 
65.3 
90.67 



Considered a non-metal. 



22 METALS 

The metals vary in their degree of usefulness; some are 
met with in e very-day life, while others are mere curiosities. 

The following seventeen metals are used to a greater or 
less extent in the metallic condition. These are: 

Antimony, Mercury, 

Aluminum, Nickel, 

Bismuth, Platinum, 

Copper, Tantalum, 

Gold, Tungsten, 

Iridium, Silver, 

Iron, Tin, 

Lead, Zinc. 
Manganese, 

For dental purposes, the following metals are of the most 
importance, namely: 

Antimony, Mercury, 

Aluminum, Nickel, 

Bismuth, Platinum, 

Copper, Silver, 

Gold, Tin, 

Iridium, Tantalum, 

Iron, Tungsten, 

Lead, Zinc. 

Eighteen are more or less extensively used in medicine 
and in the arts as coloring pigments and for alloying pur- 
poses. These are: 

Antimony, Lithium, 

Arsenic, Manganese. 

Barium, Mercury, 

Bismuth, Potassium, 

Cadmium, Sodium, 

Calcium, Tungsten, 

Chromium, Titanium, 

Cobalt, Uranium, 

Copper, Zinc. 

The remaining metals are of very little or no practical use 
in the metallic state. 

The metallurgist classifies the metals into two classes — 
the noble and base metals. A noble metal is one that forms 
unstable oxides, and is reduced from their oxides by simply 



Platinum group 



METALS 23 

heating to redness. Base metals, on the other hand, form 
stable oxides, and it requires the presence of certain sub- 
stances, known as "reducing agents," before they may be 
freed from combination with oxygen, when heated to redness. 
The noble metals consist of the platinum group, together 
with gold, silver, and mercury. 

Symbols. At. Wt. 

Platinum Pt 195.2 

Osmium Os 190.9 

Iridium Ir 193.1 

Palladium Pd 106.7 

Rhodium Rh 102.95 

Ruthenium Ru 101.7 

Gold . . . ". • . Au 197.2 

Silver Ag 107.88 

Mercury Hg 200.6 

The elements are also classified into families or groups, 
according to their atomic weights; this forms a basis for the 
"periodic classification" or the so-called "law of Octavos." 
According to this classification we have the "alkali metals" 
(sodium, potassium, lithium, etc.); "alkali earth metals" 
(calcium, barium, strontium, etc.) ; zinc, copper, aluminum, 
iron, tin, antimony and gold-platinum groups. 

Finally, metals may be classified according to their 
behavior in solution toward certain reagents, as in the five 
or six groups of qualitative analysis. We mention the 
various ways in which the metals may be classified to show 
how indefinite the question often asked, "How are metals 
classified?" seems to a person who has made a study of this 
subject. 

The metals occur in nature widely distributed, and may be 
found in the metallic condition, "native state," in combina- 
tion and as impurities in other metallic substances. 

The native metals generally contain admixtures of other 
metals — rarely are they found in the pure condition. The 
natural occurring compounds of the metals are known as 
minerals. A mineral may be defined as " a natural occurring 
compound of a metal formed by inorganic nature, generally 
possessing a definite crystalline form." The native metals 



24 METALS 

and also minerals are often associated with earthy impurities. 
These impurities are known as gangue, vein-stuff, or chat. 

An ore is a material containing one or more metals in the 
free or combined state. This term is generally restricted 
to a material bearing some metal in paying quantities. The 
difference between an ore and a mineral is that the latter is 
a chemical compound, while the former may be composed 
of two or more minerals or the elementary metal as a complex 
mixture. 

The third source of metals which in some instances is very 
important is the presence of a metal in an ore in which some 
other metal predominates. Gold as an impurity in iron and 
lead ores, silver in lead ore, and cadmium in zinc ores, 
illustrates this mode of occurrence. 

It has been estimated that 99 per cent, of the earth's crust 
consists of nine elements in the following proportions: 



Oxygen . 


. . 49.98 


Calcium . 


. 3.51 


Silicon 


. . 25.30 


Magnesium . 


. 2.50 


Aluminum 


. . 7.26 


Sodium 


. 2.28 


Iron ... 


5.08 


Potassium 


. 2.23 






Hydrogen 


. 0.94 



Practically none of these exist in the free state, but com- 
bined for the most part as silicates and oxides and, with 
rarer elements, as carbonates, haloids, and sulphates. The 
unoxidized substances, such as sulphides, are comparatively 
rare. 

Identification of Metals in their Ores. — The physical prop- 
erties of the mineral is examined, such as the crystal form, 
hardness, and lines of cleavage. A blow-pipe analysis is next 
made; this consists of bead tests, charcoal block reactions, 
and flame tests. The wet methods of qualitative analysis 
is generally used to confirm the findings of the blow-pipe. 
As a rule the dry methods of analysis is used by the pros- 
pector, and are sometimes spoken of as field tests, because 
they are made at the site w T here the ore is discovered. The 
chemical laboratory is an absolute necessity for the perform- 
ance of the wet tests. 



TREATMENT OF ORES 



25 



Quantitative Methods. — These are also classified into wet 
and dry methods. 

Assaying is that science which enables ns to find out of 
what a substance is composed, and the proportions, by 
means of dry reagents and heat. 

The wet methods are divided into two classes: 

(a) Volumetric analysis, using solutions of definite strength, 
known as standard or normal solutions. 

(b) Gravimetric analysis, precipitating the element and cal- 
culating the quantity present from the weighed precipitate. 

UNDHARD [ftTEHTED] KOMINUTER. 




Fig. 1 



Treatment of Ores. — The ore is crushed to reduce it to a 
suitable size. A ball-mill may be used, or some other form 
of machine which accomplishes the same purpose. The ball- 
mill (Fig. 1) consists of an iron drum which is caused to 
revolve. On the inner side there are step-like projections, 
and iron balls; in some cases Iceland pebbles are placed 
inside the drum, and when the drum revolves the pebbles 
or balls crush the ore against the projections. The ground 
ore sifts through screens located between each projection 
and is collected below the mill. 

The next treatment is to concentrate the ore, and for this 
purpose the crushed ore is treated with water and run over 



26 METALS 

gravity tables (gig tables) , the earthy material of less specific 
gravity passes to one side, and the heavier metal-bearing 
ore to another side of the table. The concentrates are then 
subjected to some of the following processes in order to 
further remove impurities or aid in the reduction. 

Calcination. — The object of this process is to remove 
organic impurities and water; by heating to a low red heat 
it renders the ore more porous. 

Roasting. — Roasting consists in heating to a higher 
temperature, expelling substances which can be volatilized, 
such as arsenic, sulphur, carbon dioxide, etc. The metals, 
as a rule, are reduced to their oxides as the result of this 
process. 

Sublimation. — Sublimation is the process of heating a sub- 
stance until it volatilizes and the vapor is collected as a solid. 
Arsenic, arsenious oxide, ammonium chloride are substances 
which may be sublimed. 

Distillation. — Distillation is a similar process of boiling, 
but the vapor collects as a liquid. Mercury, zinc, cadmium 
may be distilled. 

Smelting. — Smelting is a process of refining a metal-bearing 
substance by fusing. It is necessary at times to remove 
foreign material present in an ore by chemical means. 
During the smelting process these materials become oxi- 
dized, and the nature of these oxides determine the material 
which must be added to remove them. If the oxides are 
of an acid nature, such as silica, it will be necessary to add 
a substance of a basic nature, such as lime-stone. At the 
temperature of the furnace, the calcium oxide formed com- 
bines with the silica, forming calcium silicate. 

CaCOs + Si0 2 = CaSiOs + C0 2 . 

The calcium silicate is a fusible glass, and rises to the 
top of the crucible, and is spoken of as a fusible slag. If, on 
the other hand, the impurities present are basic oxides, then 
an acid material like silica or the silicates are added. 

A substance which possesses the property of combining 
with the impurities present in an ore, thus forming a fusible 



REGULUS 27 

slag, is called a flux. There are two varieties of fluxes: 
acid and basic fluxes. 

In soldering we use a flux, the object being to remove 
any oxide which may be formed, due to the heating of the 
metallic surface. (See Soldering.) 

Lixiviation. — Lixiviation is a process of washing an ore 
to remove soluble compounds. Low-grade copper ores are 
roasted with sodium chloride, then washed or lixiviated, and 
the soluble copper chloride is recovered from the water by a 
precipitation method. 

Desiccation. — Desiccation is simply heating an ore to a 
temperature slightly above the boiling point of water in 
order to dry the ore. 

Regulus. — Regulus is a term applied to certain sulphides 
formed during the process of smelting in the presence of 
sulphur. Iron, copper, or silver ores when smelted in the 
presence of sulphur form a regulus. Speiss is the arsenides 
of certain metals formed during fusion, while Matte is a term 
embracing both of these and includes sulphides, arsenides, and 
antimonides of the metals formed during fusion. 



CHAPTER III. 
PROPERTIES OF THE METALS. 

A metal may be defined as an elementary substance, 
usually solid at ordinary temperature (except mercury, a 
solid below —39.44° C), crystalline in nature, insoluble in 
water, fusible by heat, and possessing a peculiar luster, 
commonly spoken of as "metallic luster." 

To these qualities must be added those of conducting 
heat and electricity which the metals possess to the greatest 
extent, and the power of the metals, with a few exceptions, 
of replacing the hydrogen of an acid. They form basic 
oxides with oxygen and finally give off positive ions in 
solution. ' 

Such substances as arsenic and selenium lie on the border- 
line between metals and non-metals. Arsenic is sometimes 
called a metalloid, while selenium is, as a rule, placed in the 
sulphur group of non-metals. 

Fusibility. — There is a great range in the fusing points of 
the metals (mercury fusing at the temperature of —39.44° C), 
and at the other extremes we have certain members of 
the platinum group that require the greatest heat to fuse. 
The following is a list of fusing points of metals: 

Metals Fusing below Incipient Red Heat (525° C). 

Centigrade Fahrenheit. 

Mercury -39.44 -38.55 

Potassium +62.5 4-80.5 

Sodium 95.6 140.0 

Lithium 180.0 356.0 

Tin 232.0 450.0 

Bismuth 270.0 518.0 

Cadmium 320.0 608.0 

Lead 326.0 618.0 

Zinc 415.0 779.0 

Antimony 425.0 797.0 

Arsenic volatilizes before fusing . . 450.0 841.0 

Tellurium 452.0 845.0 



BOILING POINTS 



29 



Metals Fusing at Red Heat (From 700° to 900° C.). 

Centigrade. Fahrenheit. 

Aluminum 654.5 1230.0 

Magnesium 800.0 1472.0 





Metals Fusing above Red Heat. 




Centigrade 




Fahrenheit. 


Silver 960 







1760.0 


Gold 1120 








2012.0 


Copper 1200 


2192.0 


rALS Fusing at Highest Heat of Forge, or 


above White Hi 


(1300° C). 








Centigrade. 






Fahrenheit 


Manganese . . . 1242.0 






2268.0 


Cast iron 






1250.0 to 1300.0 




2300 


to 2350 . 


Pure iron 






1600.0 to 1804.0 




2913 


Oto 3400.0 


Nickel 






1450 . 






2632.0 


Cobalt . 






1500.0 






2732.0 


Palladium 






1500 . 






2732.0 


Platinum 






1753.0 






3200.0 


Rhodium 






1946.0 






3524.0 


Ruthenium 






(less than Osmium) 








Tantalum 






2770.0 






5018.0 


Iridium . 






2300.0 






4172.0 


Osmium . 






2500.0 






4532.0 


Chromium 






2000.0 






3632.0 


Tungsten 






3100.0 






5600.0 



The fusing points of metals above red heat must be 
considered only approximately, as the physical condition of 
the metal, and also the method made use of, in determining 
these temperatures, have a great influence upon the figures 
arrived at to represent their melting point. 

Incipient red heat is generally considered about 525° C; 
dull red, about 700° C; cherry red, 900° C; deep orange, 
1100° C; white, 1300° C; dazzling white, 1500° C. 

Boiling Points. — As a rule very little is known of the 
metals in the state of vapor. The boiling points are so 
high that it is impossible to observe the nature of the vapor, 
as we do not possess a substance which can withstand these 
extremes of temperature and at the same time be trans- 
parent. 

Some of the more readily volatilized metals are: zinc, 
cadmium, mercury, arsenic, tellurium, potassium and sodium; 



30 



PROPERTIES OF THE METALS 



while a few others impart a characteristic color to the flame 
when heated and are probably volatile to a limited extent. 

Under ordinary temperatures of the blow-pipe some of 
the metals do not appear to become volatile, and these are 
called "fixed" metals. Gold, copper, nickel, etc., belong to 
this class. 

Gold volatilizes when it contains other metals, but in the 
pure state it requires an extremely high temperature. Gold 
containing admixtures of copper, lead, or silver, volatilizes 
at a temperature slightly above the fusing point of the alloy. 

The following is a list of a few metals whose point of 
volatilization has been determined: 



Lead . 


327° C. 


Aluminum 






1800° C 


Mercury . 


. 357° 


Manganese 






1900° 


Cadmium 


. 756° 


Silver 






1955° 


Zinc . 


916° 


Chromium 






2200° 


Magnesium . 


. 1120° 


Tin . . 






2270° 


Bismuth . 


. 1420° 


Copper . 






2310° 


Antimony 


. 1440° 


Iron . 






2450° 


Gold . . 


. 2200° 








a- 


[. c 


. Greenwood.) 



Metallic Luster. — All metals possess this property, and 
their opacity in all probability causes the reflection of the 
light rays from their surfaces, the effects of which is to pro- 
duce a luster. Metallic surfaces not only cause the refraction 
of light but also of heat. This is taken advantage of in the 
construction of heating devices. Furnaces have been con- 
structed, consisting of metallic mirrors in which heat waves 
are allowed to be reflected from their surfaces. These mirrors 
are concave in shape and the heat waves are focussed upon a 
common point, and in this manner a great concentration of 
heat is obtained. 

The reflecting power of a substance is its property of throw- 
ing off a greater or less proportion of the heat reaching a sur- 
face, and is measured by the ratio of heat reflected to the 
incident quantity, or the heat reflected, divided by the quan- 
tity of heat received by the surface. The following is a list 
of the reflecting powers of some metallic substances : 



CONDUCTIVITY OF HEAT 



31 



Polished brass 100 

Silver 90 

Steel . . 70 

Lead 60 

Glass 10 

This power of substances of reflection is of great importance 
in the operation of soldering. When an investment material 
is used it frequently happens that a metallic piece may be 
ruined by the action of the reflected heat from the surfaces of 
the investing material. 

Conductivity of Heat. — The metals are the best conductors 
of heat but they vary with each other; some possessing this 
property to a remarkable extent. There are two methods of 
determining the conductivity: in one method the rise in 
temperature of various metals is compared by the use of 
a thermometer, and then a comparison is made, using the 
conductivity of silver as 1000. The following is a list of con- 
ductivities as determined by this method : 



Silver 

Copper 

Gold 

Brass 

Zinc 

Tin 

Iron 



1000 


Steel . . 


736 


Lead 


532 


Platinum 


231 


German silver 


190 


Bismuth 


145 


Mercury 


120 


(Wieden 



116 
85 
84 
63 
18 
13 



The figures determined by this method are only approxi- 
mate. A much more accurate method of determining this 
physical property of metals is by determining the quantity of 
heat which is conducted by a metal in a given unit of time. 
The following figures are the result of determination in which 
the number of calories of heat which are conducted by the 
various metals in a second of time are used as the standard, 
silver being taken as 100 : 



Silver 
Copper 
Gold . . 
Aluminum 
Zinc . 
Iron . 



100.0 


Tin 


94.6 


Platinum 


66.5 


Lead . 


31.1 


Antimony 


27.5 


Bismuth 


14.4 


Mercury 



13.7 
10.4 
7.3 
4.0 
1.8 
1.8 



32 PROPERTIES OF THE METALS 

The thermal conductivity of the metals is of some impor- 
tance to the dentist, as it must be taken into consideration in 
various operations about the mouth. Metallic fillings being 
good conductors of heat, convey the various changes of tem- 
perature occurring in the mouth more readily than tooth 
substance and as a result thermal insults are conveyed to the 
dental pulp and may result in the production of inflammatory 
changes in this organ. Prosthetic substitutes are subject to 
the same conditions : gold used as a base for artificial dentures 
will convey the thermal changes more readily to the mucous 
membranes than vulcanite, as may be seen by a comparison 
of their thermal conductivities : gold being represented by the 
figures 66.5 and ebonite (vulcanite) 0.034. 

Expansion by Heat. — When metals are heated they expand, 
and this property varies with the metal under consideration. 
Each metal possesses its own degree of expansibility. This 
may be represented by measuring the amount of expansion 
in one direction — linear expansion; in two directions, super- 
ficial expansion; in three directions, cubical expansion. The 
former may be used in determining the latter, and will be 
the only measure considered. 

The following is a list of linear expansions between 0° and 
100° C: 

Platinum 0.000008842 

Platinum (0° and 1000°) 0.00001015 

Copper 0.000017182 

Gold 0.00001466 

Nickel 0.000016 

Silver 0.000019097 

Tin 0.00002173 

Aluminum 0.00002313 

Lead . . 0.000028575 

Zinc 0.000029417 

Bismuth 0.000013 

Cadmium 0.000012 

Iron 0.000012 

Mercury 0.000181 

Antimony 0.000017 

There is generally a change in volume of a metal when it 
passes from the solid to the liquid state and the volume is 
altered during the fall of temperature between the point at 



EXPANSION BY HEAT 33 

which the metal solidifies and until the temperature of the 
atmosphere is reached. Antimony, bismuth and copper are 
said to expand upon solidifying, and they also impart this 
property to their alloys. These metals are added to or 
admixed with other metals for the purpose of overcoming the 
contraction which occurs during the cooling process; by so 
doing a more perfect reproduction of a model in metal may be 
obtained. In considering the property of most metals of 
contracting upon cooling, great care must be exercised in 
pouring a molten metal into a mold : if the metal be poured 
at a temperature far above that of its fusing point, there will 
be a maximum amount of contraction produced when the 
metal is allowed to cool. To overcome this objectionable 
feature it is best to pour the molten metal at that tempera- 
ture just above the melting point at which the metal just 
begins to lose its fluidity about the edges of the melting pot ; 
or a better method is to use a pine stick and ascertain the 
point at which no vibrations are felt when the stick is im- 
mersed into the molten metal. This latter process is very 
serviceable in the case of casting zinc or lead in 'the con- 
struction of dies or counter-dies. 

By comparing the coefficient of expansion of the metals 
with that of glass or porcelain bodies it will be found 
that platinum (with a coefficient of 0.000008842) and glass 
(0.000008513) are more nearly equal than in the case of any 
other metal with glass. The importance of this statement lies 
in the fact that it is often necessary to seal metals in glass or 
porcelain and it is impossible to obtain a perfect union of the 
metal and glass through the range of temperature that they 
have to pass if the metal contracts at a different rate than the 
glass or porcelain. The high cost of platinum during recent 
years has stimulated a great amount of research in this line of 
investigation to find some suitable substitute for platinum. 
It is frequently seen that alloys are made use of as a substitute 
for platinum in this capacity, in which the alloy has changed 
its form during the cooling process at such a rate that an 
imperfect joint between the alloy and the porcelain body 
results. 



34 



PROPERTIES OF THE METALS 



Porcelain teeth have been constructed in which the proper 
regard for this physical property of metals has been disre- 
garded ; the result, as might have been expected, was that the 
teeth lacked the proper resistance to the crushing force during 
mastication, and the pins of the teeth also were acted upon by 
the secretions of the mouth. 

Another very interesting feature in regard to the applica- 
tion of this physical property of metals is the consideration 
of gold during the construction of cast inlays. Special pre- 
cautions are taken in this operation, so as to prevent the 
shrinkage of the gold from changing the form of the inlay to 
such an extent as to render the inlay useless. In the con- 
struction of bridges it is necesary to prevent the shrinkage of 
the solder from changing the relative positions of the 
individual crowns which go to make up the piece. In exten- 
sive bridges the piece is soldered in sections and these in turn 
are then soldered together and in this way there is a minimum 
of force produced during the solidification and cooling of the 
solder; this in a great way prevents the contraction of the 
metal from warping the bridge. 

Conductivity of Electricity. — Metals are the best conductors 
of electricity and are considered as a type for conductors; 
non-metals in some instances do not conduct a current and 
are said to be non-conductors. The temperature and also the 
purity of the metal has a direct influence upon its conducting 
powers of electricity. The following is a comparative list of 
the conductive powers of the various metals for electricity : — 

14.36 

13.44 

11.91 

11.25 

8.15 

4.14 

1.55 

1.12 



Silver 


100.00 


Palladium 


Copper . 


92.08 


Platinum 


Copper (hard) . 


90.05 


Nickel 


Gold . . . 


66.84 


Tin . . 


Aluminum . 


58.01 


Thallium 


Magnesium 


33.70 


Antimony 


Zinc .... 


25.52 


Mercury 


Lead . . 


18.76 


Bismuth . 


Cadmium . 


14.64 





The conducting power of the metals is best measured by a 
comparison of the resistance which the metals offer to the 
flow of a current. By considering this phase of the subject 



REPLACING THE HYDROGEN OF AN ACID 35 

absolute figures are obtained, while in the above list only a 
comparison is made. In considering the conductivity we 
assume that the flow of electricity through a conductor is 
analogous to the flow of heat; the flow of electricity being 
caused by a potential difference, as in the case of heat, it is 
due to a difference of temperature. The unit of resistance is 
taken as the resistance offered to an unvarying current by a 
column of mercury at the temperature of melting ice, 
14.4521 grams in mass, of a constant cross-sectional area, and 
of a length of 106.3 centimeters. The cross-sectional area is 
1 square millimeter. 

The resistance of a wire of uniform section = p — , 1 = 

s 

length, s = cross-section, p = the specific resistivity of the 
metal. 

The resistance of a metal increases as the temperature 
increases, the specific resistance may then be obtained for the 
various temperatures by the following equation R t = Ro 
(15 + xt) where x = the temperature coefficient. 

The following is a table of specific resistance of the metals 
expressed in microhms at 15° C. (Dewar and Fleming), also 
a table of temperature coefficients: 

P in microhms, Temperature 

15° C. coefficient. 

Platinum 10.917 0.00367 

Gold 2.197 0.00377 

Silver . . . 1.468 0.00400 

Copper 1.561 0.00428 

Aluminum 2.667 0.00435 

Iron 9.056 0.00625 

Nickel 12.323 0.00622 

Tin 13.048 0.00440 

Zinc ■ 5.751 0.00406 

Lead 20.380 0.00411 

Replacing the Hydrogen of an Acid. — Most metals are soluble 
in the ordinary acids; the hydrogen being replaced and a salt 
of the metal formed. Hydrochloric acid reacts with a metal 
with the formation of a metallic chloride and the liberation of 
hydrogen, 

Zn + 2HC1 = ZnCl 2 + H 2 . 
2Fe + 6HC1 = 2FeCl 3 + 3H 2 . 



36 PROPERTIES OF THE METALS 

Sulphuric acid is peculiar in its action upon certain metals 
and there may be two classes of reactions produced. 

(a) In which hydrogen and a sulphate of the metal is 
formed, Zn+H 2 S0 4 = ZnS0 4 +H 2 . 

(b) In which sulphur dioxide, water and a sulphate of the 
metal is formed, Cu+2H 2 S0 4 = CuS0 4 +S0 2 +2H 2 0. 

Nitric acid is far more complex in its reaction upon metals 
and the products formed are dependent upon the strength of 
the nitric acid and the property of the metal attacked. 
Hydrogen is rarely given off in the molecular condition, as the 
oxidizing power of nitric acid is so great that the moment 
hydrogen is liberated from combination it is oxidized to 
water (H 2 0). As nitric acid is used extensively for dissolving 
metals, and also as it is the best solvent for them, the following 
will serve to illustrate a few of the important reactions of this 
acid upon metals : 

(a) 3Cu+8HN0 3 = 3Cu(N0 3 ) 2 +4H 2 0+2NO. 

(6) 4Zn+10HNO 3 (dil) =4Zn(N0 3 ) 2 +5H 2 0+N 2 0. 

(c) 4Zn+9HN0 3 (cone) =4Zn(N0 3 ) 2 +3H 2 0+NH 3 . 
Antimony and tin are peculiar in their reaction with nitric 
acid; instead of the nitrates these metals form oxides and 
for this reason nitric acid is never used to dissolve these two 
metals when a solution containing antimony or tin is desired. 

Platinum, gold, ruthenium, osmium, rhodium and iridium 
do not replace the hydrogen of an acid. With the exception 
of rhodium and iridium they are attacked by aqua regia (3 
parts hydrochloric acid and 1 part nitric), but this is not by 
the replacement of hydrogen. Selenic acid (H 2 Se0 4 ) is said to 
dissolve gold and the noble metals; however, this reaction is 
not made use of in the study of the metals. 

Basic Oxides. — The prevailing idea is that metals form basic 
oxides only, but this, however, is not the case; all basic oxides 
are metallic oxides, but all metallic oxides are not basic. 
Chromium, manganese, iron and quite a few other metals 
form acid oxides. Those metals which form both varieties of 
oxides are said to possess acid and basic properties. 

Ionization. — When the salts of the metals are dissolved in 
water they are broken up to a certain extent into extremely 



IONIZATION 37 

fine particles called ions, which are of two varieties, (a) con- 
sisting of the metallic portion of the salt molecule, (b) con- 
sisting of the acid radicle. The metallic ion possesses the 
power of conducting a positive electrical charge (and in fact 
do possess a positive charge) when a current is passed through 
such a solution and is consequently known as a positive 
ion; on the other hand, the acid radicle ion is called the nega- 
tive ion because it conveys the negative charge under like 
conditions. 

The metallic salts are called electrolytes because of their 
property of conducting an electric current and may be dis- 
tinguished from other substances by this fact. In very dilute 
solutions it is possible to have all of the salt ionized, while 
in more concentrated solutions there is a point of solubility 
for the salt in the molecular and also for the ionic con- 
dition. Considering how a substance is ionized, the following 
reactions will represent this phenomenon in its simplest 
form: 

+ 

HCl = H - CI 

+ + -- 
H 2 S0 4 = HH - SO4 

+ 
HNO3 = H - NO3 
+ 
H(C2H302) = H — C2H3O2 

The degree of ionization is dependent upon the substance 
under consideration, the halogen acids are more completely 
ionized than the other acids and for this reason are considered 
the strongest of acids. 

+ - 

NaCJ = Na CI 

+ + - - 
Cu(N0 3 ) 2 = Cu N0 3 N0 3 

+ + -- 
Z11SO4 = Zn S0 4 

The above reactions represent how the metallic salts are 
broken up into ions when in solution. 



38 PROPERTIES OF THE METALS 

When a metal is acted upon by an acid the following illus- 
trates the ionic condition of the substances : 

+ + -- ++ -- 

Zn + HH S0 4 = Zn S0 4 + H 2 

The positive zinc ion replaces the positive hydrogen ion 
forming zinc sulphate, and the ions of which combine, the 
hydrogen ions at the same time discharge their positive charge 
and combine to form molecular hydrogen which leaves the 
solution as a gas, if the zinc sulphate formed is in such quan- 
tity as to exceed the degree of ionization of this salt it will 
crystallize from solution. 

A solution of sodium chloride may be prepared and then 
hydrochloric acid gas passed through the solution ; the sodium 
chloride will change from the ionic condition to the molec- 
ular state and will then fall out of solution. The phenome- 
non may be. explained by the fact that hydrochloric acid is 
more readily broken up into its ions than sodium chloride; this 
causes the sodium ion to combine with the chlorine ion. 

Another condition which may exist is that of a salt of a 
metal, say copper chloride, in solution to which metallic iron is 
added; the iron in this case goes into solution as Fe ions and 
the copper is deposited as metallic copper. The following 
ionic reaction represents the change : 

+ + -- ++-- 

Cu C1C1 + Fe = Fe C1C1 + Cu. 

The two positive charges of the copper ion is given up, the 
copper ceases to be an ion and assumes the molecular condi- 
tion at the same time the iron takes up these positive charges 
as the iron (Fe + -f ion). 

This reaction is used in obtaining metals from solution, and 
the following will illustrate a few other reactions of this type: 

+ - ++ - - 

2(Ag N0 3 ) + Cu = Cu N0 3 N0 3 + 2Ag. 
+ + - - ++ - - 

Hg N0 3 N0 3 + Cu = Cu N0 3 N0 3 + Hg. 



IONIZATION 39 

Ionic Chemical Changes. 

1. Disunion and combination of ions. When a metallic 
salt is dissolved in water there is a disunion of the ions 
of which it is composed and upon evaporating the solution 
combination again occurs with the formation of molecules 
of the salt. 

2. One ion may displace another. It has already been 
stated that the metallic ions may replace the hydrogen of an 
acid; one acid radicle may also replace another, as is shown by 
chlorine replacing bromine and iodin from their compounds. 
Metals react in the same manner toward each other, and the 
metallic elements may be arranged according to this property 
in a series designated as the electromotive series. The 
following is a list of metals arranged in this manner : 

+ 

1. Alkali metals. 

2. Alkali earth metals. 

3. Magnesium. 

4. Aluminum. 

5. Manganese. 

6. Zinc. 

7. Chromium. 

8. Cadmium. 

9. Iron. 

10. Cobalt. 

11. Nickel. 

12. Tin. 

13. Lead. 

14. Hydrogen. 

15. Arsenic. 

16. Copper. 

17. Antimony. 

18. Bismuth. 

19. Mercury. 

20. Silver. 

21. Palladium. 

22. Platinum. 

23. Gold. 



40 PROPERTIES OF THE METALS 

Some very interesting information may be gained by a close 
study of this list of metals as they are arranged, the metals 
occupying positions near the positive end will replace a metal 
located lower in the list from combination. The metals 
above hydrogen are classed as positive while those below are 
classed as the negative ones, as regards their behavior toward 
the metals above hydrogen. 

Metals Nos. 1, 2, 3 are unstable in air; Nos. 1, 2, 3, 4 are not 
reduced from their compounds (oxides) by heating in a stream 
of hydrogen; Nos. 1 to 13 never occur in the free state in 
nature, they replace the hydrogen ion of an acid, and Nos. 4 
to 13 are the base metals which form stable oxides. Nos. 15 
to 23 do not replace the hydrogen of acids, found in the free 
state in nature, while Nos. 19 to 23 are the noble metals and 
form unstable oxides. 

When two of the metals are immersed in a solution of an 
electrolyte in which one of the metals is more readily acted 
upon than the other by the solution, a so-called voltaic couple 
is formed, the greater the distance between the metals in the 
electromotive series the greater will be the potential difference 
existing between the metals. This principle is made use of in 
the construction of a wet cell. If two metals are placed in the 
mouth in which there exists a great potential difference, an 
electric current will be produced ; this current is found to have 
a direct action upon tooth structure, particularly if the metals 
are fillings in the teeth. 

The saliva contains inorganic salts in solution which act as 
electrolytes. 

Much agitation has been created recently in regard to the 
employment of such metallic combinations in dental amalgam 
alloys and the question as to the deleterious effects of these 
alloys is still subject to dispute; from a practical point of 
view, however, such alloys should not be used. 

The explanation why some of the metallic oxides are basic 
oxides is rather simple, when it is considered that, a "base" 
is a substance which liberates negative hydroxy] ions on 
solution. 



FARADAY 1 S LAW 41 

When a metallic oxide is treated with water the following 
phenomenon takes place: 

Na 2 + H 2 = 2NaOH + - 

Sodium hydroxide is ionized as follows: Na OH 

This same reaction may be written for any of the basic oxides. 

Electrolysis. — When an electric current is passed through a 
solution of an electrolyte the current is carried through the 
solution by the ions of the salt. The metallic elements con- 
vey the positive charge from the positive electrode to the 
negative electrode and may then be discharged; at the same 
time the negative ions of the salt convey the negative elec- 
tricity to the negative pole and are discharged. The metallic 
ions are thus found at the negative pole (cathode) and are 
called cations, while the negative ions found at the positive 
pole (anode) and are called anions. 

The electrical power consumed in this operation is exceed- 
ingly small and advantage is taken of this in obtaining 
metals from their compounds. The metals so obtained are in 
an exceedingly high state of purity. 

Faraday established the fundamental laws on electrolysis 
and the subject of electrolysis would hardly be complete with- 
out mentioning these in explanation of this phenomenon. 

Faraday's Law. — When the same quantity of electricity is 
passed through different electrolytes the ratio between the 
quantities of the liberated products of electrolysis is the same 
as that between their chemical equivalent. 

If solutions of silver nitrate, gold chloride and copper 
sulphate be introduced into the same electric circuit it will be 
found that the metals will be deposited at the cathode and in 
such quantities as their equivalent weights, that is, their 
atomic weight divided by their valency in the compound; 
thus: 108 grams of silver, 31.7 grams of copper and 65.66 
grams of gold. 

The quantity of electricity required to liberate 1 gram of 
hydrogen taken as the unit, then the number of units required 
to liberate the atomic weight of the various other elements 
may be obtained by dividing the equivalent weights of the 
elements into their atomic weights. 



42 PROPERTIES OF THE METALS 

The quantity of electricity which is carried by one gram of 
hydrogen as the unit was determined as 96,540 coulombs. Then 
when an element is represented with two plus marks it signi- 
fies that such element will carry 2 times 96,540 coulombs of 
electricity. 

If it be required to deposit 108 grams of silver in one hour 
the amperage of such a circuit may be determined by dividing 
the coulombs (96,540) by the time in seconds (60X60) giving 
27.9 amperes of current strength necessary for such a deposit 
in the time mentioned. 

From these facts the following facts were developed : 

(1) The mass of the ions liberated at either pole is propor- 
tional to the quantity of electricity which passes any section 
of the circuit. 

(2) The mass of the ions liberated at either pole is propor- 
tional to the chemical equivalent of the ion, i. e., atomic weight 
divided by the valency of the element in the compound. 

It would take us too far into physics to develop these laws, 
although electrolysis is of importance in the recovery of 
metals, electroplating and other metallurgical operations. 
Those especially interested in this phase of the subject may 
consult text on physic and electrochemistry. 

Potential Difference. — The metals have a certain solution 
tension which tends to force them into solution. This force 
or tension gradually diminishes from the positive to the 
negative end of the electromotive series. If the ions of the 
metal are present in the solution already, they tend to give up 
their electrical charge and deposit themselves upon the metal. 
The tendency of the metal ions to be deposited and give up 
their charge is directly due to their osmotic pressure in the 
solution. The osmotic pressure of a solution containing the 
molecular weight in grams of a salt is 22.4 atmospheres. 

Determinations have been made with normal solutions, i. e., 
those containing the equivalent of one hydrogen in grams of 
the salt to the liter of water. A bar of the metal was 
immersed in the solution of its salt and in this condition it is 
found that the metallic ions in the solution possess a positive 
charge, while the metallic bar has a negative charge. 



POTENTIAL DIFFERENCE 



43 



+1.21 


Lead 






. -0.13 


+1.00 


Hydrogen . . . -0.28 


+0.80 


Copper (Cu it) 


-0.61 


+0.49 


Arsenic . 


-0.62 


+0.14 


Bismuth 






-0.67 


+0.06 


Mercury- 






-1.03 


+0.04 


Silver 






-1.05 


-0.04 


Palladium 






-1.07 


-0.04 


Platinum 






-1.14 


-0.08 


Gold . 






-1.35 



Potential Differences in Volts for Normal Solutions of Cations 
(Alex. Smith). 

Magnesium 
Aluminum . 
Manganese . 
Zinc . 

Cadmium . 
Iron (Fe ir) 
Thallium . 
Cobalt . . 
Nickel . 
Tin . . . 

If a strip of silver be placed in a solution of silver nitrate 
(normal solution) the silver ions from the nitrate possess a 
positive charge and the strip of silver a negative charge; the 
difference between these two charges determines the electrical 
condition of the solution, in this case the solution will be 
found to have a negative charge of — 1.05 volts. 

Considering two of these metals immersed in a solution, 
such for example as sulphuric acid, it will be found that the 
following couples produce very nearly the following values : 



Silver-zinc, 
Copper-zinc, 
Tin-zinc, 
Mercury-zinc, 



1.05 + 0.49 = 1.54 volts 

0.61 + 0.49 = 1.10 volts 

0.08 + 0.49 = 0.57 volts 

1.03 + 0.49 = 1.52 volts 



In testing dental amalgams Crandall reports the following 
figures for amalgams containing zinc and compares these 
figures with those in which a non-zinc dental amalgam alloy 
was used, in the amalgam, 

Zinc alloy amalgams range from 20 to above 25 millivolts. 

Non-zinc amalgams ranged from 1.75 to 2 millivolts. 

These figures were obtained from amalgams free from cor- 
rosion of the saliva, after the fluids of the mouth had acted 
upon the amalgam the zinc amalgams showed a smaller 
deflection of the galvanometer than before. 

The subject of electrolysis and ionization is attracting much 
interest at the present time in dentistry and it is well to bear 
in mind the difference between the two terms. Whenever a 



44 



PROPERTIES OF THE METALS 



metallic salt goes into solution, ionization is produced, but for 
electrolysis to be produced an electric current must be passed 
through the solution. 

Odor and Taste. — Odor and taste are possessed by a few 
of the metals. Iron, copper and zinc when heated evolve 
peculiar odors. Iron when treated with acids sometimes 
evolves an odor, but this is due to hydrocarbons as impurities 
in the iron. Arsenic gives off an alliaceous odor (garlic-like) , 
and the recognition of which is one means of detecting arsenic. 
Odor and taste may in some instances be explained : as in the 
case of alloys, or the presence of two metals in the mouth, 
forming a voltaic couple, compounds of the metals would be 
formed, which would affect the taste buds on the tongue. A 
similar phenomenon, in the case of mixing amalgams in the 
hand, producing metallic compounds, gives rise to an odor. 

Specific Heat. — When metals are heated they take up 
heat. The quantity necessary to raise them through one 
degree of temperature differs in each individual metal. 
The quantity of heat necessary to raise one gram of metal 
through 1° C. of heat is called its specific heat. Water has 
the greatest capacity for heat, and the quantity of heat 
necessary to raise it through 1° C. is taken as the stand- 
ard. The following is a list of specific heats of the metals 
between 0° and 100° C: 

Aluminum . . . 0.2143 

Antimony . . . 0.0513 

Arsenic .... 0.0822 

Bismuth . . . 0.0308 

Cadmium . . . 0.0567 

Cobalt .... 0.1067 

Copper .... 0.0968 

Gold .... 0.0324 

Iron 0.1138 



Lead 






0.0314 


Magnesium 




0.2475 


Mercury- 




0.0332 


Nickel . 






0.1092 


Platinum 






0.0324 


Potassium 






0.1655 


Silver 






0.0570 


Tin . . 






0.0555 


Zinc 






0.0950 



The specific heat of water is taken as 1000 and it requires 
one calorie of heat to raise the temperature of one gram of 
water through 1° C, then from the above table it will require 
the corresponding number of calories of heat to raise a gram of 
the metal through 1° of temperature, or it might be explained 
by using some metal, say gold for example, with a specific 
heat of 0.0324, then it will require 0.0324 calorie of heat to 



SPECIFIC GRAVITY 45 

raise one gram of gold through 1° centigrade. The specific 
heat of the metals depends upon their physical condition, hard 
copper differs from the softer variety in its specific heat. The 
temperature has also a direct influence upon this property of 
the metals, the specific heat is greater between 200° and 300° 
than between 0° and 100°. Any agency which tends to in- 
crease the density of a substance diminishes its specific heat. 
The specific heats of the metals are of value for two pur- 
poses; they indicate the quantity of heat which is necessary 
to raise a metal through a given range of temperature, and 
secondly, they are of importance in proving the atomic weight 
assigned to a metal is correct. The specific heat divided into 
6.4 gives approximately the atomic weight of the metal, for 
example, 

6 4 

Gold sp. heat = 0.0324, then ' = at. wt. 197.5 
. 0o^s4 

and the atomic weight of gold by experimentation is 197.2. 

The factor 6.4 is obtained by multiplying the atomic weight 
of the elements by the specific heat ; this figure is the average 
for determinations made upon the various elements and is 
called the atomic heat. 

Specific Gravity. — This term denotes the comparison of the 
weight of equal volumes of two substances under the same 
conditions of temperature, one of them being taken as a 
standard. For solids and liquids, distilled water is the 
standard. It is the tendency to drop this term at the present 
time as the density of a substance in metric weights also 
expresses its specific gravity. If the volume of a substance 
is known then, by simply weighing it in the metric system and 
calculating the weight of a cubic centimeter we also have 
the specific gravity. 

Density = — . 

volume 

The specific gravity of a metal is, as a rule, not subject to 
change, but the physical condition of the metal tends to 
alter its specific gravity. Precipitated, cast, and rolled gold, 
all have different specific gravities. 

The lightest metals belong to the alkali group; they are 
lighter than water, and at the other extremes osmium is 



46 



PROPERTIES OF THE METALS 



generally considered one of the heaviest of elements. The 
following is a list of specific gravities: 



Lithium . 






0.59 


Cobalt . 






8.5 


Potassium 






0.875 


Cadmium 






8.6 


Sodium . 






0.97 


Molybdenum 






8.6 


Rubidium 






1.52 


Nickel 






8.8 


Calcium . 






1.58 


Copper . 


8.8 


to 8.9 


Magnesium 






1.74 


Bismuth . 






9.82 


Aluminum 






2.56 


Tantalum 






10.8 


Zirconium 






4.15 


Thorium 






11.1 


Selenium 






4.3 


Palladium 






11.5 


Vanadium 






5.5 


Rhodium 






12.1 


Arsenic . 






5.67 


Ruthenium 






12.26 


Tellurium 






6.25 


Uranium 






18.7 


Antimony 






6.72 


Tungsten 






19.2 


Chromium 






6.8 


Platinum 






21.5 


Zinc . 


6 


S6 


to 7.2 


Iridium . 






22.42 


Tin . . 






7.29 


Osmium . 






22.48 


Manganese 






7.4 


Lead . 






11.38 


Iron . 


7 


7 to 8.1 


Mercury 






13.59 


Silver . 10 


42 to 10.52 


Gold . . 


19.3 


Thallium 






11.9 











Color. — The color of the metals depends upon the physical 
condition in which they exist. In the compact form, as we 
usually see them, they present a range of color from white of 
silver to deep blue of lead. The color of compact metals 
can be classed as follows: 





Silver 
Mercury 


Pale yellow 


f Barium 
\ Strontium 


White < 


Zinc 
Tin 








Sodium 


Deep yellow 


Calcium 




Aluminum 










Rich yellow 


Gold 




( Lead 






Blue 


Platinum 


Pink 


Copper 




Iron 








Antimony 







In powder, or amorphous form, their color becomes entirely 
changed; gold becoming brownish yellow; silver, grayish 
white; copper, yellowish red; and platinum, black. 

Some of the metals can be obtained in an extremely fine 
divided state, as a colloidal solution, and when viewed with 
the ultramicroscope the solution proves to be a suspension 
of shining metallic particles. Under this condition platinum 



COLOR 47 

makes a brown solution; gold, bluish red; silver, when dry; 
bluish or green; silver, when dissolved in water, deep red, 
mercury, black. 

Colloids have been defined as substances in solution which 
could be separated from crystalloids by dialysis. Mathews 
has classed the colloidal metals as suspensoids, because they 
do not possess the property enabling them to gel, and further- 
more, has classed colloids into two groups, viz., emulsoids and 
suspensoids. The colloids being defined as substances which 
in solution gives particles ranging from 1 to 100 uu (uu = one 
thousandth of a micron) in linear dimensions. 

The following is the size of some of the metals in this 
condition : 

Gold . 6 to 130 uu. 

Silver 50 to 77 uu. 

Platinum 44 uu. 

The particles of a colloidal metal in solution are electro- 
negative. 

In the vapor form the metals in some instances impart 
colors to the flame, as in the so-called flame or spectroscopic 
tests. In most cases these colors are produced by the vapor 
of a volatile compound of the metal rather than the metal 
themselves. 

Potassium gives violet flame. 
' Sodium gives yellow flame. 
Lithium gives red flame. 
Barium gives yello wish- green flame. 
Calcium gives reddish-yellow flame. 
Copper gives green or blue flame. 
Tellurium gives pure green flame. 
Thallium gives pure green flame. 
Zinc gives whitish flame. 
Arsenic gives light blue flame. 
Strontium gives scarlet flame. 

By means of the spectroscope these metals may be posi- 
tively identified by the characteristic color bands produced. 
These bands may be recognized even in the case of mixtures 
of the various metals. This is the only positive method of 
identifying such metals as those belonging to the alkali group, 
as they do not, as a rule, give characteristic precipitates with 
the various reagents usually used in analytical chemistry. 



48 PROPERTIES OF THE METALS 

Malleability, Ductility, and Tenacity. — The qualities of 
malleability, ductility, and tenacity differ widely in the 
metals. The term malleability, when applied to such a 
metal as gold, signifies that by hammering or rolling its 
surface may be extended in all directions, and that it is 
capable of being thus reduced to very thin leaves or sheets 
without fracture of its continuity at the edges during the 
process of attenuation; when applied to other metals the 
term should be understood as expressing this quality 
relatively. Gold is the most malleable of the metals and is 
capable of being made into leaves of s^ i^so °f an mcn m 
thickness, each grain of which will cover a surface of seventy- 
five square inches. 

The property of malleability and that of brittleness are 
directly dependent upon the hardness and crystalline con- 
dition of the metals. Bismuth, antimony, and arsenic, which 
are absolutely crystalline metals, are so brittle that they 
fly to pieces when struck with the hammer, and they can be 
finely powdered in a mortar. Formerly malleability and 
ductility were considered as essential properties of a metal, 
but this is no longer the case, as bismuth and antimony 
disprove the rule. 

Malleability also presupposes a certain degree of softness, 
toughness, and a total obliteration of crystalline structure. 

The degree of malleability is greatly influenced and de- 
pendent upon the temperature. Most of the metals become 
more malleable and softer when heated. Iron, for instance, is 
most malleable at red heat. Zinc is crystalline and not very 
malleable at ordinary temperatures, but at 100° to 150° C. 
it is quite malleable, and at 200° C. it again becomes brittle. 
Frozen mercury is also malleable. 

There are no methods of determining the absolute values of 
malleability and ductility; however, the lists published give an 
idea of what may be expected of a metal when submitted to 
the processes of rolling or being passed through the draw 
plate. As to the absolute values of a table of this kind, it is 
found that our methods of measuring these properties fail 
before the limit of malleability or ductility has been reached. 

Malleability, ductility, and tenacity depend upon the 



MALLEABILITY, DUCTILITY, AND TENACITY 49 

property of cohesion and that phase of cohesion known as 
solid flow. The mechanical procedures used in rolling, 
drawing, or the application of forces tending to cause the 
rupture of a metal cause the rearrangement of the molecules. 
In the case of some metals the crystalline structure permits of 
the rearrangement without overcoming the force of cohesion 
of the molecules. The effect of these distorting forces 
produces an abnormal condition between the molecules and as 
a result the metals become more brittle. Heating the metals 
after such treatment tends to restore the original softness to 
the metal. 

In the following list by Regnault 1 the metals are arranged 
in the order of their malleability: 

1. Gold. 8. Zinc. 

• 2. Silver. 9. Iron. 

3. Tin. 10. Nickel. 

4. Copper. 11. Palladium. 

5. Cadmium. 12. Potassium. 

6. Platinum. 13. Sodium. 

7. Lead. 14. Mercury (frozen). 

Ductility signifies that property which renders a metal 
capable of being drawn into rods or wires, usually accom- 
plished by passing an elongated piece of metal through a 
series of gradually diminishing holes in a steel draw-plate ; the 
granular particles of the metal are thus extended into fibers. 
One grain of gold has been drawn into a wire 550 feet long. 
To accomplish this result a compound wire is made of 
gold covered with silver, the tenacity of the latter being 
taken advantage of to enable the gold to be carried through 
the successive holes of the draw-plate until the greatest 
possible attenuation is reached; after which it is immersed 
in nitric acid, which dissolves the silver, leaving a gold 
wire 5-0V0 °f an mcn m diameter. By the same method 
Wollaston drew out a platinum wire -3 o~oVo"o °f an mcn m 
thickness. 

All malleable metals are ductile, but malleability and 
ductility are not necessarily proportional to each other. 

Ductility depends upon toughness and tenacity, otherwise 
the force needed to draw a metal through the draw-plate 

1 Phillips's Metallurgy, p. 412. 
4 



50 PROPERTIES OF THE METALS 

would rupture it. Heat affects ductility, rendering some 
metals quite workable and decreasing this property in others. 
Hammering and drawing change the molecular structure of 
metals and greatly influence their physical properties, 
rendering them denser, harder, more elastic, and brittle. 
In rolling plate and drawing wire it is necessary to keep the 
metals at their proper degree of softness, therefore we must 
anneal them frequently. 

In the following table the metals are arranged according 
to the ductility: 1 



1. 


Gold. 


6. Zinc. 


2. 


Silver. 


7. Tin. 


3. 


Platinum. 


8. Lead. 


4. 


Iron. . 


9. Nickel. 


5. 


Copper. 


10. Palladium. 

11. Cadmium. 



Tenacity is the power possessed by metals to sustain 
weight, and to resist rupture, when a bar or rod is exposed 
to tension. Various kinds of tenacity are recognized accord- 
ing to the nature of the externally acting force: ordinary 
tenacity, resistance to traction; relative tenacity, resistance 
to fracture; reactive tenacity, resistance to crushing; shear- 
ing tenacity, resistance to lateral displacement; torsional 
tenacity, resistance to twisting. 

As the fitness of metals for certain purposes in the industrial 
arts depends largely upon this property, it is of the utmost 
importance to know the comparative tenacity, not only of 
the different metals but of the different alloys. 

In determining the comparative tensile strength of metals 
it is customary to take bars of the metals of equal length 
and equal diameter and to determine the number of pounds 
weight required to cause their rupture. This is usually 
accomplished by means of a testing machine constructed 
on the compound-lever principle. 

In subjecting metal bars or wires to a certain amount of 
tension, an elongation of the wires takes place. If this 
degree of tension is not overstepped they will return to their 
original length; but if the tension is carried beyond this 

1 Platinum should be classed above gold in accord with Wollaston's 
determinations. 



MALLEABILITY, DUCTILITY, AND TENACITY 51 

point a permanent elongation takes place, in which case the 
elastic limit of the metal has been passed. In the technical 
use of metals where they have to withstand great strains, 
as in elevator ropes or in chains, it is of the utmost impor- 
tance that the strain should never go beyond the elastic 
limit, because certain molecular changes take place in the 
metals, resulting from the permanent elongation. These 
changes greatly weaken the tensile strength of the metals 
and might result in accidents. 

Tensile strength is diminished by continuous strain. If a 
wire is subjected to a low strain continuously it will finally 
break, when a much greater strain would not have caused 
its rupture at first. Tenacity is also influenced by the shape 
of the body; for instance, a hollow cylinder is much stronger 
than a solid one, provided the quantity of metal is the same 
in both. 

Elevation of temperature, even within rather circumscribed 
limits, affects the tenacity of metals to a marked degree, 
generally diminishing it. 

Alloying increases tensile strength, as is instanced in the 
case of brass, which has a greater tenacity than either of its 
components, copper and zinc. Heat destroys this property 
greatly. 

The following table 1 gives the results of experiments on 
the tensile strength of a few of the metals at temperatures 
between 15° and 20° C. : 

For Wire of 1 sq. mm. Section, Weight (in Kilos) Causing 

Permanent elongation 

of 1/2000. Rupture. 

Gold, drawn 13.5 27 

Annealed 3.0 10 

Silver, drawn 11.3 29 

Annealed 2.6 16 

Platinum, drawn 26 . 37 

Annealed 14.0 23 

Copper, drawn 12.0 40 

Annealed under 3.0 30 

Iron, drawn 32.0 61 

Annealed under 5.0 47 

Palladium, drawn 18.0 37 

Annealed under 5.0 27 

1 Annales de chimie et de physique (III), vol. viii, W T ertheim. 



52 PROPERTIES OF THE METALS 

The following table shows the relative order of the metals 
in their capacity for sustaining weight : 

1. Iron. 5. Gold. 

2. Copper. 6. Zinc. 

3. Platinum. 7. Tin. 

4. Silver. 8. Lead. 

It has been observed that students and others very often 
fail at first to appreciate the difference between these prop- 
erties, and they not infrequently fall into the mistaken idea 
that the three qualities of malleability, ductility and tenacity 
are possessed to an equal extent by each metal. If, however, 
we take gold for example — the most perfectly malleable and 
ductile of the metals — we shall find that in tenacity it ranks 
considerably below some of the others, and the greatest 
care is necessary in drawing a piece of gold into even a 
moderately fine wire, and beyond a certain limit, past which 
platinum or copper may be carried with safety; gold would 
not possess sufficient tenacity to overcome the resistance 
to which it would be exposed in passing through the smaller 
holes of the draw-plate, and fracture would result. 

Iron, on the other hand, which exceeds all of the other 
metals in tenacity, is in malleability inferior to gold, silver, 
copper, platinum, lead, zinc, tin, and cadmium. 

It is stated that brass drawn into wire will often, after a 
time, become crystalline in texture and brittle by slow change 
of molecular arrangement. 1 

Hardness. — Hardness is that property of the metal which 
resists a change in the relative position of the molecules of 
the metal without separating them from each other. 

Hardness may therefore be tested and recorded as the 
resistance to indentation. 

There are a number of methods for testing hardness, but 
the one of Ballentine is probably the best, and depends upon 
the following fact: that a known and constant weight, which 
is allowed to fall through a known and constant distance, 
will exert a known and constant force upon an anvil, which, 

1 Makins's Metallurgy, p. 10. 



CRYSTALLIZATION 53 

if the force is transmitted to a pin which is capable of indent- 
ing the material tested, the relative hardness of the materials 
can be determined by the depth of the indentation. 

Density Hardness. — By this is understood the hardness 
produced in pure metals or alloys by compression, rolling or 
hammering. The hardness of a metal is not necessarily 
proportional to its density. The densest metals may be 
either hard or soft, as shown in the case of iridium (specific 
gravity 22.4), which is a fairly hard metal, while gold (specific 
gravity 19.3), platinum (specific gravity 21.5), and lead 
(specific gravity 11.38) are certainly very soft. Experiments 
show that density hardness, produced by compression, 
depends upon both ductility and strength of a metal. 

Original Hardness after 

hardness. compression. 

Copper, cast 6 20 

Brass, cast 12 26 

Brass, hard .30 35 

Iron, wrought 18 30 

Iron, gray 40 41 

Steel, annealed 30 45 

Zinc 8 20 

Type metal 20 21 J' 

Babbitt metal 5 6J 

Babbitt metal, extra hard 9 8 

Lead 2 3 

These figures show the copper gaining 300 per cent, in 
hardness by compression, while the cast Babbitt metal 
loses some of its initial hardness. 

The study of compression hardness is of prime importance 
in selecting metals for bearings which will be subjected to 
great shocks or compression. 

Crystallization. — Crystallization is the process by which 
the molecules of a substance arrange themselves in geo- 
metrical forms when passing from a liquid or gaseous to the 
solid state. Many substances are capable of crystallization. 
The crystals formed are very definite in their characters, 
and can be used like any other physical properties in dis- 
tinguishing one substance from another. Some substances 
crystallize in two distinct forms, and they are then said to 
be dimorphous. The outward shape of a crystal is its most 
striking feature, but this form is only an external expression 



54 



PROPERTIES OF THE METALS 



of a regular internal structure. Many crystals occur in very 
complicated forms, so that at first sight it would seem 
impossible to recognize them, but by careful study they can 
be simplified and referred to one of six systems. To be able 
to classify and compare the forms of crystals we must have 
some simple mode of expressing the relative positions and 
inclinations of their planes. This is accomplished by referring 
them to systems of axes, according to the method of analytical 
geometry. The position of any crystal plane is thus fixed 
by and expressed in the relative lengths of its intercepts in 
the axes to which it is referred. The axes to which the planes 
of a crystal are referred, called the crystal! ographic axes, 
may be of equal or unequal length, and may intersect at 
either oblique or right angles. The six crystal systems are: 

1. The Isomeiric or Regular System. — All the forms refer- 
able to this system have three axes (imaginary lines passing 
through the solid angles of the octahedron) of equal length, 
intersecting at right angles. 

Examples: Regular octahedron, hexahedron (cube) rhom- 
bic dodecahedron, etc. 




Fig. 4. — Rhombic 
dodecahedron. 



Fig. 5.— Tetra- 
hexahedron. 



Fig. 6. — Trisoc- 
tahedron. 



CRYSTALLIZATION 



55 



2. The Tetragonal or Quadratic System. — All forms refer- 
able to three axes at right angles to each other, two of equal 
length, the third or principal one having a variable length. 

Examples: Tetragonal pyramids, tetragonal prisms. 



Fig. 7 





Figs. 7 and 8. — Tetragonal pyramids. 



Fig. 9 

— r- 



-~^ 



__U- 



Fig. 10 



—J- 



-J— -L 



Fig. 11 



i 



Figs. 9, 10 and 11.— Tetragonal prisms. 



3. The Hexagonal System. — All forms referred to four axes 
— three lateral axes of equal length, inclined at angles of 
60 degrees to each other, one principal axis at right angles 
to the other three and having either the same or a different 
length. 



56 PROPERTIES OP THE METALS 

Examples: Hexagonal pyramid and hexagonal prism. 




fCC^>i 



^ 



Fig. 12. — Hexagonal pyramid. Fig. 13. — Hexagonal prism. 

4. The Orthorhombic System. — All forms referable to three 
axes of unequal length intersecting at right angles. 

Examples : Orthorhombic prism and orthorhombic pyramid. 




:fe^4— 



Fig. 14. — Orthorhombic pyramid. 



Fig. 15. — Orthorhombic 
prism. 



5. The Monoclinic or ObJiqve System. — All crystals have 
axes of unequal length — two at right angles to each other 



CRYSTALLIZA TION 57 

and the third at right angles to one and inclined to the 
other. 

Examples: Monoclinic pyramids and prisms. 

6. The Triclinic or Asymmetric System. — The crystals be- 
longing to this system are referred to three axes of unequal 
length, all inclined to one another. 

Examples: Triclinic prisms and pyramids. 



Fig. 16. — Monoclinic pyramid. Fig. 17. — Triclinic pyramid. 

It is stated that under favorable circumstances all the 
metals will assume a crystalline form. It is known that some 
of them, as gold, silver, etc., are found native as cubes or 
octahedra, or in slight modifications of these forms; and 
metals in a crystalline form may be obtained by electrolysis, 
as, for instance, silver or lead, while a condensation of the 
vapors of zinc or cadmium will produce crystals of these 
metals. Metals with low fusing points, such as bismuth or 
antimony, will crystallize on cooling after they have been 
melted. Nearly all the metals yield crystals when deposited 
from their solutions by electric currents of feeble intensity. 
The beautiful preparation known as Watt's Crystal Gold is 
formed in this way. Gold so prepared is generally in a high 
state of purity. 

Highly crystalline metals exhibit peculiar appearances on 
their fractured surfaces. These are quite constant for the 



58 



PROPERTIES OF THE METALS 



individual metals, and can be taken as indicating the purity 
of the metals. The varieties of fractures are: 

1. Crystalline: as zinc, antimony, and bismuth. 

2. Granular: steel. 

3. Fibrous: wrought iron. 

4. Silky: copper. 

5. Columnar: grain-tin. 

6. Conchoidal: native arsenic. 



Native metals crystallize in the following systems: 



Palladium 
Arsenic 
Magnesium 
Antimony 
Zinc 

Bismuth 
Gold . 
Silver . 



Rhombohedral 



Isometric 



Lead 

Copper . 

Mercury (solid) 

Platinum . 

Iron 

Tin . . . . 

Potassium . 



Isometric 



Quadratic 



Sonorousness. — Sonorousness may be denned as that prop- 
erty possessed by a substance of emitting a sound when 
struck. Most of the metals in a pure state do not possess 
this property, but upon alloying with other metals acquire 
it. Aluminum is an exception to the rule and is used instead 
of parchment in drum-heads. One of the first articles con- 
structed of aluminum was a child's rattle for one of the 
nobility of Europe. To show the effects of alloying upon 
metals, iron does not possess this property until combined 
with the proper amount of carbon, when it will be found that 
it gives off a musical sound when struck. Tin and copper, 
neither being sonorous, when alloyed form bell metal. 

Elasticity is that property possessed by a substance by 
virtue of which it returns to its normal position after a 
disturbing force has been applied. The measure of elasticity, 
so-called coefficient of elasticity, is determined by the follow- 
ing formula: 

stress 



Coefficient of E 



stress 



A substance which requires the greatest force to produce 
the least distortion will evidently have the greatest coeffi- 



MAGNETISM 59 

ciency. The popular belief that rubber is the most elastic 
substance is an error, because the smallest amount of stress 
will produce a great strain, and on referring to the above 
formula it will be seen that the coefficient will be small. 

Platinum is added to gold, although both metals have a low 
coefficient of elasticity; the resulting alloy possesses elas- 
ticity to such an extent that it is used for clasps for artificial 
dentures. Platinum and iridium alloy — the iridium being 
present in small quantities — forms an elastic alloy, which is 
sometimes used for the construction of metallic bases for 
artificial dentures. 

Magnetism. — Although the ancients were aware of the fact 
that when magnetite or loadstone was brought near or in 
contact with iron, there was an attractive force which held 
them together so that a variable degree of tension was 
required to pull them apart; furthermore, that this property 
was transmitted from the loadstone to the iron; nevertheless, 
it was only after the invention of the mariner's compass that 
magnetic science made any progress. 

A magnet has two poles, and if it is suspended so that it 
can swing freely, these poles will always arrange themselves 
in a definite relation to the geographical axis of the earth, 
one pointing north, the other south. 

Whenever an electric current flows in a closed circuit the 
surrounding space becomes a field of magnetic force, and any 
piece of iron in it will become inductively magnetized. Such 
an arrangement of an electric circuit and iron is called an 
electromagnet. 

When magnetism is induced, a certain proportion of 
magnetism usually remains after the inducing force is 
removed. This happens even with the softest iron, if the 
inducing force is very great. In different bodies the power 
of retaining magnetism varies as much as the inductive 
susceptibility. Thus, while the inductive susceptibility 
of steel is less than that of iron, it retains much more of the 
magnetism imparted to it, and the harder the steel is tem- 
pered the greater will be the coercive force or retaining 
power. Increase in temperature diminishes magnetism, and 



60 PROPERTIES OF THE METALS 

red heat destroys it in all bodies but cobalt, the latter 
requiring a white heat to effect this result. 

The two varieties of magnetism spoken of as paramagnet- 
ism and diamagnetism, respectively, mean attraction or 
repulsion to the magnet. 

Paramagnetic metals are iron, nickel, cobalt, manganese, 
chromium, palladium, platinum, and osmium. 

Diamagnetic metals are bismuth, antimony, zinc, tin, 
cadmium, sodium, mercury, lead, silver, copper, gold, etc. 

The magnetism of metals is undoubtedly largely influenced 
by impurity. The commercial copper, for example, is para- 
magnetic owing to the presence of traces of iron; but when 
it is reduced by means of zinc from chloride or sulphate, it is 
diamagnetic. 

Agents which May Volatilize a Metal. — Concentration of 
solar rays in the focus of a lens; the voltaic current; the 
oxy hydrogen blow-pipe flame; oxyacetylene blow-pipe flame. 

M. Depretz employed the first three in conjunction, by 
which means he volatilized magnesium, and with a powerful 
Bunsen battery alone he reduced carbon by volatilization 
to the state of a black powder. 1 

Opacity. — Opaque bodies do not transmit light. No bodies 
are absolutely opaque; however, metals, as a rule, absorb 
the rays of light which fall on them, and a few allow some of 
the rays to pass through. Gold in a highly attenuated con- 
dition transmits green light; silver and a few others also 
transmit light. 

Occlusion. — Occlusion is that property possessed by a 
metal of absorbing gases. 

The metals, though destitute of physical pores, possess 
the property of absorbing gases either on their surfaces or in 
their mass. This may be observed when a metal is heated 
and then allowed to cool in contact with the gas. Platinum 
occludes four times its volume of hydrogen and 4.15 volumes 
of carbon monoxide. Silver, reduced from the oxide, absorbs 
about seven times its volume of oxygen, and nearly one 

1 Percy's Metallurgy. 



WELDING 61 

volume of hydrogen when heated to dull redness in these 
gases. 

Palladium absorbs 980 times its volume of hydrogen at red 
heat, and at ordinary temperature 376 times its volume. 
The following list shows the volume of hydrogen absorbed 
by some of the metals: 1 



Palladium, black . 


502.35 


Nickel 


. 17.57 


Platinum, sponge . 


49.3 


Copper . 


4.5 


Gold . . . . 


46.3 


Aluminum . 


2.72 


Iron . . . 


19.17 


Lead . 


. 0.15 



Molten silver occludes about twenty-two times its volume 
of oxygen, which is given up again (with the exception of 
0.7 volume) on solidification. As the mass cools, the oxygen 
evolved often bursts through the outer crust of solidified 
metal with considerable violence, ejecting portions of the 
still liquid silver as irregular excrescences; this is known as 
the spitting of silver. Small quantities of admixed metals 
prevent the absorption of oxygen. 

This fact must be borne in mind when silver is used in 
cast work. I have had several inquiries as to the cause of 
failure on the part of practitioners in using silver to cast 
root restorations. 

Welding. — Welding is the process of joining two metallic 
surfaces by the aid of heat and pressure. Pure gold may be 
welded in the cold. Iron requires a white heat in order to 
be welded. 

Fusion or Autogenous Welding. — Fusion or autogenous 
welding is accomplished by an intense heat concentration 
at the location of the weld. Its object is to bring the metal, 
at the point of treatment, to a liquid state, so that the two 
bodies of metal to be joined will flow or fuse together, as 
distinguished from the joint made by pressure or blows. 
Fusion welding, as usually practised, employs heat generated 
either by electricity or by the burning of a combustible gas 
with oxygen. For the combustible gas, hydrogen, coal gas 
or acetylene is generally used. 

1 Neuman and Stientz. 



62 PROPERTIES OF THE METALS 

Electric Welding. — There are two distinct forms of electric 
welding, commonly known as the resistance and arc pro- 
cesses. 

Goldschmidfs Process of Welding. — When a mixture of 
finely divided aluminum is mixed with certain oxides (iron 
oxide or chromium oxide) and the mass ignited by a fuse, 
the aluminum takes the oxygen from the other metallic 
oxides, liberating these metals in a fused condition. The 
temperature of about 3000° C. is reached in a very short 
period of time. This process is sometimes spoken of as 
"thermite welding." 

Swaging. — Swaging is the process of adapting a lamina of a 
metal to conform to a desired shape, by the uses of a die and 
counter-die by pressure. 

Forging. — Forging is a process of hammering a metal into 
various shapes. Both of these processes are dependent 
upon the physical power of the molecules of a metal known 
as "solid flow." The molecules of a metal by virtue of 
"solid flow" may change their relative positions without 
overcoming the force of cohesion. 

Flotation. — Flotation is the process of adding oils to metal- 
bearing substances during the operation of concentrating 
ores. By this process it is found that certain minerals may 
be recovered from tailings and in this manner cause a more 
complete recovery of the metal from its ores. This branch 
of metallurgy has been but recently developed and some of 
the peculiarities of the process are that certain oils when 
agitated with minerals cause a frothing; the oil contains 
the mineral of some certain metal. For example, an Qre 
containing zinc and lead; an oil may be used which will 
cause the flotation of the zinc and the lead will not be acted 
upon, and on the other hand, another oil would cause the 
flotation of the lead. The character of these phenomena is 
not thoroughly understood and it cannot be predicted which 
oil will cause a flotation with any certain metal. Experi- 
mentation alone will determine this point. 

Atomic Volume. — The atomic volume of the metals is some- 
times made use of in the process of alloying. Attempts are 



ATOMIC VOLUME 



63 



made in this manner to bring about a more perfect equilib- 
rium between the atoms of the metals entering the alloy. 

The atomic volume of the metals is determined by dividing 
the atomic weight by the specific gravity. The figures do not 
express the comparative volumes of the atoms of the sub- 
stance but the space occupied by the atoms plus the inter- 
atomic spaces. 

The following is a list of atomic volumes (Price & Fahren- 
wald) : 



Aluminum 

Antimony 

Bismuth 

Cadmium 

Chromium 

Copper 

Gold . 

Iridium 

Iron 

Lead 



10.4 


Mercury 


. 14.0 


18.1 


Molybdenum 


. 10.6 


21.2 


Tungsten 


9.8 


13.0 


Nickel 


. 6.5 


7.5 


Osmium . 


. 8.4 


7.1 


Palladium 


. 8.9 


10.2 


Platinum 


9.06 


8.6 


Silver 


. 10.2 


7.1 


Tin . . . 


. 16.3 


18.2 


Zinc . 


9.2 



In constructing alloys of the metals, as a rule the propor- 
tions are calculated according to mass or weight; however, if 
it be desired to consider the atomic structure, so that the 
conditions present in the alloy will more nearly approximate 
the condition present in a chemical compound, a nearer 
approach to this condition can be obtained by a consideration 
of the atomic volumes of the metals. 



CHAPTER IV. 
ALLOYS. 

An alloy is a substance formed by the bringing together 
of two or more metals in the state of fusion. 

The phenomenon which takes place when metals are 
brought together in the state of fusion is a very complex 
one. According to the older views on this subject the 
resulting substance may be (Matthiessen) : 

1. A solution of one metal in another. 

2. A chemical compound. 

3. Mechanical mixture. 

4. A solidified solution or mechanical mixture of two or all of the above. 

Our present conception of alloys is that they may consist of : 

1. Similar crystals of one metal. 

2. Mixed crystals of different metals. 

3. Chemical compounds of different metals. 

4. Eutectics of different metals. 

5. Mixtures of the above. 

The kinetic theory of matter states that matter is made 
up of molecules and molecular spaces. The molecules are in 
a state of constant motion. There are two factors at 
work upon the molecules: molecular motion and the force 
which tends to bind the molecules together— cohesion or 
adhesion. 

By a simple study of these forces the various physical 
properties of a metal or alloy may readily be explained. 

The physical state of a metal or alloy depends upon the 
balance between these forces. When a metal is heated, 
the movement of the molecules is increased, and when the 
two forces become equal, viz., the force of cohesion and 



ALLOYS OF TWO METALS 65 

free movement of the molecules, the metal becomes a liquid 
or fuses. 

It requires heat energy to produce this change, and as the 
temperature of a substance is the "external evidence of 
internal molecular motion," then the average velocity of the 
molecules will determine the temperature of the substance. 
In the change from the solid to the liquid state the velocity 
of the molecules must be increased, and so long as the 
substance remains a liquid at a constant temperature this 
velocity is constant. It requires a considerable quantity of 
heat to change a solid substance at the temperature of its 
melting point to a liquid with an equal temperature. To 
illustrate: Ice at 0° C. requires 80 units of heat to convert 
it to water at 0° C. 

When a metal or alloy passes from the solid to the liquid 
state a quantity of heat is taken up, so-called "latent heat," 
as energy of the molecule, and when passing from the liquid 
to the solid condition this same quantity of heat is given off. 

The following numbers have been obta'ned for the latent 
heats of fusion of the substances specified: 





Calories. 




Calories. 


Water 


. 80.00 


Cadmium 


. . 13.66 


Zinc . 


. 28.13 


Bismuth . 


. . 12.64 


Platinum 


. 27.18 


Lead . 


. . 5.37 


Silver 


. 21.07 


Mercury 


. . 2.83 


Tin . . . 


. 14.25 







ALLOYS OF TWO METALS. 

Absolute Immiscibility. — If two metals are alloyed, which 
are not miscible, they will separate according to their specific 
gravities, and upon solidifying it will be found that the 
lower portion of the mass will be made up of crystals of the 
metal having the greatest specific gravity, while the upper 
portion of crystals of the lighter metal. 

Mixed Metals. — When two metals of different fusing points 
are alloyed, and the force of adhesion of the molecules is 
greater than the force of cohesion — i. e., the attraction of the 
5 



66 ALLOYS 

molecules of a metal for themselves is less than their attrac- 
tion for the molecules of the other metal — a condition exists 
in which we have a mixture of crystals. The mixed crystals 
begin to form at a temperature lower than that of the 
highest fusing metal. In some cases lower than the lowest 
fusing constituent metal. The alloy is said to be a "solid 
solution" and is homogeneous in appearance. 

Chemical Compounds. — Two metals may be brought to- 
gether, and as a result they unite chemically, giving a 
metallic compound possessing entirely different physical prop- 
erties. There has been a union between the atoms of the 
metals, and the crystalline form of this compound is entirely 
different from that of the component metals. The force 
which binds them together is entirely different from cohesion 
and adhesion, but the force of cohesion now binds the newly 
formed molecules together, and when the alloy crystallizes 
it will contain one variety of crystals throughout. 

Eutectics. — A eutectic may be defined as that mixture in 
an alloy that has a definite melting point lower than the 
constituent metals and is of uniform crystalline structure. 

A fused alloy containing two metals, A and B, is cooled; 
that quantity of A or B will separate out, which is in excess, 
in respect to a mixture consisting of A and B in definite 
quantities. This continues with the fall of temperature 
until a certain point is reached; at this point the mixture 
AB separates out at the same time and in such proportions 
that the melting point and the composition of the liquid 
remain unchanged. This mixture behaves like a simple 
substance, for it exhibits a constant melting point, although 
it is only a mixture. This mixture is called a eutectic mixture. 
This term eutectics is not limited to alloys, and the same 
condition is met with in solutions of non-metallic substances. 
The philosophy of eutectics may be explained as follows: 
The two metals are soluble in each other to a certain extent, 
that is, the force of adhesion between the different molecules 
is greater than cohesion; as the result of this, mixed crystals 
will be formed, made up to the extent of their solubility. 
This result is the formation of a mixture having a different 



ALLOYS OF TWO METALS 67 

intermolecular force: Between these molecules there is a 
uniform condition entirely different from that existing 
between the molecules of the constituent metals. It requires 
less heat to overcome this adhesive force than it does to 
overcome the cohesion of the molecules of the free metals. 
This explains why eutectics have a lower melting point than 
the constituent metals. 

The more metals present in an alloy, the more possibilities 
in regard to the formation of eutectics; for example, in the 
case of an alloy containing three metals, A, B, C; A and B, 
B and C, and A and C may form eutectics possessing the 
characteristics as to melting point and crystal formation. 

Hardness and Fusibility. — It is often found that the 
metals do not possess sufficient hardness for commercial 
purposes. 

Alloying, as a rule, increase the hardness of metals. Gold 
and silver both being too soft for the purpose of coinage, 
when alloyed with about 10 per cent, copper attain hardness 
sufficient to withstand attrition to the degree required for 
currency. Tin and copper are alloyed, forming bronze, 
which is much harder than either of the two metals. In 
the proportion of 94 parts copper and 6 parts of tin an alloy 
is produced which is so brittle that it may be broken with a 
hammer. Antimony and bismuth are noted for their property 
of imparting hardness to their alloys. In fact, most of the 
alloys containing an appreciable quantity of either of these 
metals are brittle. 

Copper and silver are added to gold to increase elasticity, 
and the hardness of gold which per se is too soft to be used 
in the construction of gold bases and in crown and bridge- 
work. 

The fusing point of an alloy is always less than that of the 
least fusible constituent, but in quite a number of cases it is 
less than the lowest fusing constituent. In some cases the 
alloy may have its fusing point at a temperature considerably 
decreased. Bismuth, cadmium and tin are noted for their 
ability to depress the fusing points of their alloys, and there 
are combinations of these metals which fuse at a temperature 



68 ALLOYS 

less than the boiling point of water, although tin, the lowest 
fusing constituent, fuses at 232° C. An alloy composed of 
5 parts bismuth, 3 parts lead and 2 of tin melts at 91° C, 
and the addition of small quantities of cadmium further 
reduces the fusing point to 60° C. This fact is made use of 
in the construction of solders. The metal to be soldered is 
alloyed, giving an alloy with a fusing point less than the piece 
to be soldered. The metallic surfaces may then be united 
by using this lower fusing alloy without danger of fusing 
the metallic surface, which would result in ruining the piece. 
To illustrate: a gold solder for prosthetic work should fuse 
at a temperature lower than the plate upon which it is to be 
used. Such a solder should also possess the following prop- 
erties in order to fulfil all the requirements demanded of it: 

(a) Color, which should be as near that of the plate as 
possible. 

(b) Resistance to the actions of the fluids of the mouth. 

(c) Ready flow during the act of soldering. 

Density. — The density of an alloy is dependent upon the 
change which takes place in the metals during the act of 
alloying. 

The volume of an alloy may be: 

(a) Equal to the sums of the volumes of the constituent 
metals. 

(6) Less than the sum of the volumes of the metals. 

(c) Greater than the sum of the volumes. 

Consequently an alloy may expand, contract, or neither 
expand nor contract upon setting. The density will then be 

governed by (a), (b), or (c) as density = — , ,i.e., density 

equals the weight of the alloy divided by its volume. 

Alloying may change the volume of the metals, conse- 
quently the density will be altered. When the volume is equal 
to the combined volumes of the metals, the density will be 
a mean of the densities of the admixed metals. When the 
volume is less than that of the combined volumes of the 
metals (alloy contracts on solidifying), the density will be 
greater than the mean. If the volume of the alloy is greater 



ALLOYS OF TWO METALS 69 

(alloy expands), the density will then be less than the mean 
of the densities of the alloyed metals. 

Alloys possessing a greater specific gravity Alloys having a specific gravity inferior 
than the mean of their components. to the mean of their components. 

Gold and zinc. Gold and silver. 



tin. 



bismuth. " lead 



antimony. 



cobalt. " iridium 



Silver and zinc. 



iron. 



copper. 



nickel. 



" lead. Silver and copper. 

" tin. Copper and lead. 

" bismuth. Iron and bismuth. 

" antimony. " antimony. 

Copper and zinc. " lead. 

" tin. • Tin and lead. 

" palladium. " palladium. 

" bismuth. " antimony. 

" antimony. Nickel and arsenic. 

Lead and bismuth. Zinc and antimony. 

" antimony. 
Platinum and molybdenum. 
Palladium and bismuth. 



Color. — The color of an alloy is generally that of the pre- 
dominating metal. However, in some cases the alloy may 
have its color completely changed. Three conditions are 
possible : 

1. It may take the color of the predominating metal. 

2. It may take the color of a metal which does not pre- 
dominate. 

3. It may take a color entirely different from any of its 
components. 

Malleability, Ductility and Tenacity. — Malleability and 
ductility are diminished by alloying; the brittle metals in 
most cases completely destroy these properties when alloyed 
with even the most malleable and ductile of metals. In the 
cases of two malleable metals, the resulting alloy is less 
malleable than either. Example : gold and lead, or lead and 
platinum. According to Mr. Makins, antimony, when 
added to gold to the extent of ttwo parts will make gold 
unworkable. 



70 ALLOYS 

Tenacity is generally increased by alloying. The following 
results were obtained by Matthiesen, by employing wires 
of the same gauge and noting the weights which caused their 
rupture before and after alloying: 

Pounds. Pounds. 

Copper, unalloyed, 25 to 30; alloyed with 12 per cent, tin, 80 to 90 

Tin, unalloyed, under 7; 12 " copper, 7 

Lead, unalloyed, " 7; tin, 7 

Gold, unalloyed, 20 to 25; " copper, 70 

Silver, unalloyed, 45 to 50; platinum, 75 to 80 

Platinum, unalloyed 45 to 50 ; 
Iron, unalloyed, 80 to 90; steel (iron alloyed with carbon) above 200 

COMPOSITION OF ALLOYS. 

Chemical Compounds. — Staigmiiller calls attention to the 
"periodic law" in grouping those metals which form com- 
pounds with each other upon alloying. This classification 
divides the elements into seven distinct groups, arranged 
horizontally. The elements composing any vertical column 
do not form compounds with one another. An element 
forms compounds with all members of one of the groups or 
none. Lead, an exception to this, forms two chemical 
compounds with gold, but none with silver or copper. The 
following is an abbreviated list of these series: 



Li 


Cu 


Mg 


Zn 


Al 


Ge 


As 


Na 


Ag 


Ca 


Cd 




Sn 


Sb 


K 


Au 


Ba 


Hg 




Pb 


Bi 



The following is a list of some of the better known com- 
mercial alloys and their approximate composition: 

n ,. • /Gold 90.0 

Goldcom • < Copper 10.0 



Silver 



Silver 90.0 

Copper 10.0 

Copper 50.0 

German silver ....■{ Zinc . . . . . 25 . 

Nickel 25.0 

i Lead 80.0 

Type metal \ Antimony 20.0 



COMPOSITION OF ALLOYS 71 



Pewter 
Plumber's solder 



Dental alloy 



Tin 92.0 

Lead 8.0 

Tin 67 . 

Lead 33 . 

Bismuth . . ' . . . . 8.0 

Mellottes (Newton's alloy) ■{ Lead \ 5.0 

Tin 3.0 

Copper .... 67 to 72.0 

Zinc 28 to 33.0 

Tin 8 to 70 . 

Babbit metal -j Antimony . . . 2 to 17 . 5 

Copper . . . . 1 to 11.5 

Silver 75.0 

Platinum 25.0 

f Copper 6.0 

Dorrance's alloy . < Silver 2.0 

I Zinc 4.0 

[Copper 60.0 

Platinoid 1 J Zinc 24.0 

| Nickel 14.0 

[ Tungsten 2.0 

Decomposition. — The metals composing an alloy are more 
easily acted upon by acids than the pure metals. Platinum 
is insoluble in nitric acid, but silver-platinum alloys, con- 
taining up to 10 per cent, of platinum, are soluble in nitric 
acid. 

The metals, as a rule, are more readily oxidized in the 
alloyed condition. Mercury and aluminum undergo decom- 
position with the liberation of metallic mercury and an oxide 
of aluminum; the same phenomenon takes place in case of 
iron and mercury. Noble metals alloyed with base metals, 
when heated, cause the oxidation of the base metal and by 
adding a flux the base metal oxides, combines with the flux 
and is thus separated from the noble metal. 

Influence of Constituent Metals.— Mercury, bismuth, tin 
and cadmium give fusibility to alloys ; tin also gives hardness 
and tenacity; lead and iron give hardness; arsenic, antimony 
and bismuth render alloys brittle; antimony and bismuth 
overcome contraction. 

Phosphorus and arsenic when added to alloys of copper 
and tin, have the power of dioxidizing or eliminating metallic 
oxides which are invariably present. Phosphor-bronze owes 

1 Hepburn. 



72 ALLOYS 

its closeness of grain and superior tenacity to the addition 
of phosphorus, and it is claimed "when arsenic or arsenical 
compounds are made to unite, under suitable conditions, 
with alloys of copper and tin, known as bronze or gun-metal, 
it imparts to them several remarkable properties, such as 
homogeneity, hardness, elasticity, tensile strength and tough- 
ness, and a peculiar smoothness, rendering it a valuable 
antifriction metal for journal bearings," etc. 

Manganese and its compounds have a faculty of freeing 
iron of impurities, the presence of which would render the 
iron unfit for the manufacture of steel. 

Arsenic when added to lead increases the hardness and 
the fluidity of the molten lead. Advantage is taken of this 
fact in the manufacture of shot. 

Aluminum is a rather hard metal to cast, but when a small 
quantity of zinc is added the alloy more readily takes up 
the fine lines of the mold. 

Liquation may be described as the separation of a portion 
of the metals of an alloy, during the act of fusing, into new 
compounds. When an alloy is heated slowly to a temperature 
slightly above its fusing point, and is not disturbed, the 
metals may separate, forming new compounds which have a 
different fusing point. The newly formed compound will 
crystallize and if the alloy is again allowed to solidify it 
will be found that it is not uniform in construction; some 
portions will contain the newly formed compound and 
other portions will be of entirely different composition or 
crystalline form. The result will be that of a heterogeneous 
mass possessing different properties from the original alloy. 
Silver and copper alloys possess the tendency of liquating; 
the copper separates and crystallizes at the edges as the 
fused mass assumes a solid form. To overcome liquation, 
an alloy should be thoroughly stirred before pouring. A 
green stick is sometimes used by plunging it into the molten 
mass and thoroughly stirring, so as to break up these crystal- 
line formations. 

Annealing. — Annealing is the process of heating a metallic 
substance to restore its original working properties. When a 



COMPOSITION OF ALLOYS 73 

metal or an alloy is worked, i. e., rolled, hammered or drawn 
into wire, it becomes harsh. During the mechanical treat- 
ment, the molecules of the metal are caused to assume 
different positions in regard to one another. If the metal 
is then heated, the molecules are released from this strained 
condition and, upon cooling, assume their normal molecular 
relations. Most metals may be annealed by simply heating 
to a temperature short of their fusing point. Gold, copper 
and brass are annealed by heating to redness; platinum 
requires a white heat in order to have its original softness 
restored. Aluminum is generally annealed by coating it 
with sweet oil or vaseline and then burning the oily material 
from its surface. Lead, tin and zinc are best annealed by 
placing them in boiling water and allowing them to cool 
slowly. 

Temper. — When steel is heated and suddenly chilled a 
peculiar condition results; instead of the metal becoming 
soft it acquires an unnatural degree of hardness and is said 
to be tempered. 

The hardening of iron with carbon (steel) is generally 
understood to mean the heating of the metal to a high 
temperature and then plunging it into a bath for the purpose 
of suddenly cooling it. While this is true of most steels, a few 
alloying materials now used reverse this, the hardest and 
toughest state being obtained by slow cooling in the air. 

By quenching steels from high temperatures and temper- 
ing, their wearing qualities, elastic limits, tensile strength, 
magnetic qualities, and resistance to shock can be greatly 
improved, and yet they will not be so hard that they cannot 
be scratched with a file. 

The factors having an influence upon the hardness are the 
nature and composition of the metal, the temperature of the 
metal when quenched, volume and temperature of quenching 
bath. 

High temperature causes a rearrangement of molecules 
and a change in chemical composition; sudden cooling holds 
the molecules in this changed position. 

The temperature necessary to bring about the intra- 



74 ALLOYS 

molecular changes depends upon the variety of ingredients 
which have been alloyed with the steel. 

By polishing the surfaces of steels which have been 
quenched at different temperatures, and then etching these 
surfaces with picric or hydrofluoric acid a very characteristic 
configuration can be seen with the aid of the microscope. 
These appearances in steels of different kinds and tempers are 
due to the separation or combination of definite chemical 
compounds. These compounds are respectively known as 
ferrite (pure iron) ; cemetite (iron carbide) ; pearlite (intimate 
mixture of ferrite 32 parts and cemetite 5 parts) ; martensite 
(appearing as fine intersecting lines in steel containing 0.85 
per cent, carbon and which has been heated to 1400° R, 
before quenching); austentite (in steel containing 1.1 per 
cent, carbon, suddenly cooled from 2000° F.). Troostite 
and sorbite are other forms. 

In subjecting steel to different heat treatments we can 
change the constituents from pearlite to martensite, sorbite, 
autentite and troostite, and back again through these 
different stages, and by examining them with the micro- 
scope we can judge very closely the treatments to which 
they have been subjected. As these changes cause the con- 
stitution, static strength and dynamic properties to change, 
we can easily see the importance of this knowledge. 

Preparation.— The process of alloying metals is rather com- 
plex, and before any attempt is made to produce an alloy, 
the physical properties of the metals to be alloyed should 
be thoroughly studied. 

During the heating process, base metals should be melted 
in a suitable vessel, and the flame should not come in contact 
with the metallic surfaces. 

Noble metals may be alloyed with base metals in two 
ways: (1) Melting the higher fusing noble metals and 
protecting the surface by a suitable flux; then quickly 
plunging the base metal below the surface of the molten 
mass. Some metals as zinc, cadmium and antimony, when 
alloyed with metals which have a much higher fusing point, 
may be more readily alloyed by wrapping them in paper 



COMPOSITION OF ALLOYS 75 

and then plunging below the surface of the molten mass of 
the higher fusing metals. (2) The base metals may be 
fused first, then the noble metal in the form of a thin ribbon 
may be slowly added. An alloy consisting of tin and silver 
can be prepared by fusing the tin (M. P. 232° C), and then 
adding the silver (M. P. 960° C.) in the form of a very thin 
ribbon. The advantage of this method is that there is less 
danger of oxidation of the base metals. This would be lost 
from the alloy. To insure a uniform mix, it is always best 
to fuse a freshly prepared alloy a second time and to thor- 
oughly agitate the mass before pouring. 

Granulating-pouring the alloy from a height into a vessel 
of water, or rolling out the alloy, before the second fusion, 
will assist in obtaining an intimate mixture. Base metal 
alloys may have the dross (oxides), which forms on their 
surfaces during fusion, reduced by placing a hydrocarbon 
in the retort while the alloy is still in the fused condition. 

To prevent occlusion of gases by fused alloys, a specially 
constructed furnace must be used. Some inert gas like nitro- 
gen is forced into the furnace, driving out the oxygen of the 
air and thus preventing occlusion. Some metals when 
heated to their fusing point oxidize so readily that it is 
very difficult to obtain the metal in a fused condition neces- 
sary for alloying. The same form of furnace is used in this 
case as described above. 

It is sometimes necessary to have a substance present that 
will prevent the oxidation of the metals during fusion. This 
forms a protecting layer and prevents the oxygen of the air 
from coming in contact with the metallic surfaces. 

For high fusing metals fused borax or salt is commonly 
used. For low fusing metals powdered charcoal, graphite 
or hydrocarbons are made use of. 

Pouring of Fused Alloys. — The proper degree of heat at 
which an alloy should be poured is that temperature just 
above its fusing point, when it will pour readily. In pouring 
into a mold, if the metal be poured at a temperature too 
much above its fusing point, the cooling mass will contract 
until the temperature of the room is reached, thus causing 



76 ALLOYS 

an undue amount of contraction; on the other hand, if it is 
poured at a temperature too low, the alloy does not possess 
sufficient fluidity to take up the fine lines of the mold. With 
base metals, as lead and zinc, the degree of heat for pouring 
may be roughly estimated by plunging a green stick into the 
molten mass; if there is no vibration felt, the metal is in a 
proper condition to be poured. 



CHAPTER V. 
METALLURGICAL APPARATUS. 

The fuels used in metallurgical operations depend upon 
(a) their cost; (b) their availability; (c) the nature of the 
operation. 

The unit of heat value is called the calorie. A calorie 
(small c) is the quantity of heat necessary to raise the 
temperature of 1 gram of water one centigrade degree. 
A Calorie (large C) is 1000 times small c, or the heat necessary 
to raise 1000 grams of water 1 degree. 

The value of a fuel is measured by its caloric value. In 
reductions as practised in smelting works, coal, oil and 
producer gas are the principal fuels. Coal is dependent 
upon carbon and hydrogen compounds of carbon for its 
calorific value. Oil consists of a complex mixture of hydro- 
carbons. The oil is mixed with steam and forced into a 
furnace, called an oil ejector furnace; intense heat results. 
Many industries are taking advantage of this form of fuel, 
especially when intense heat is required. 

Producer Gas. — This gas is produced by the incomplete 
oxidation of coal. In its preparation the caloric value is 
considerably lessened; consequently this form of fuel is not 
so economical as some of the others. 

Fuels Used in Dental Metallurgy. — The fuels used in 
dentistry may be enumerated as follows: 

f p t 1 / Coal oil 

(a) Liquids { . , , , \ Gasoline 



(6) Gases 

(c) Electricity 



Hydrogen 
Coal gas 
Water gas 
Acetylene 



78 METALLURGICAL APPARATUS 

Coal Gas. — Coal gas or water gas is the principal fuel 
used by the dentist. Coal gas is the product of the destruc- 
tive distillation of coal, and is made up of hydrocarbons. 
Water gas is prepared by passing steam over heated coke, 
causing a decomposition of the water, and the formation of 
a mixture of hydrogen and carbon monoxide; both of these 
gases burn with a non-luminous flame, and to make them 
luminous, so that the gas may also be used for illuminating, oil 
is cracked into the gases. The carbon monoxide and hydro- 
gen are passed through a chamber filled with bricks heated 
to a bright redness, the oil is allowed to enter and a decompo- 
sition takes place, resulting in the formation of gaseous hydro- 
carbons. The composition of the finished product consists 
of carbon monoxide, hydrogen and gaseous hydrocarbons. 

Natural gas requires specially constructed blow-pipes 
in order to obtain the greatest efficiency in its use. Coal oil 
and gasoline for blow-pipe work are vaporized. In using 
gasoline every precaution should be taken to prevent the 
resorvoir tank from coming in close proximity with the blow- 
pipe or a free flame, as many accidents have resulted from this. 

Hydrogen with oxygen is used to obtain high temperatures 
in the oxyhydrogen blow-pipe for melting platinum and also 
in cast gold work. Acetylene with oxygen and also air is 
used when gas is not available, and seems to serve as a very 
good substitute. 

Electricity may be used in two ways: (a) By passing it 
through a substance which offers resistance and advantage 
taken of the heat produced. The electric furnace for porce- 
lain work is an illustration of this method, (b) By forming 
an arc, which produces intense heat; this is used in melting 
the most refractory metals. 

Electricity is also used for various other metallurgical 
purposes, i. e., (a) depositing metals from solution (electro- 
plating) ; (b) as a power to run motors, for lathes, compressed- 
air machines, etc. 

Furnaces. — Coal Furnaces. — These are of two types, de- 
pending upon the nature of the current of air used in the 
combustion of the fuel: 



HEATING DEVICES 79 

(a) Chimney draft, in which the natural air draft from a 
chimney is used. Reverboratory, open hearth, and the 
small furnaces usually used for melting base metals, are of 
this type. 

(b) Forced Draft or Blast Furnace. — In this type of furnace 
an artificial current of air is produced to accelerate the com- 
bustion of the fuel. The blast furnace as described under 
Iron, is a type of this variety of furnace. 

HEATING DEVICES. 

Alcohol. — Alcohol blow^pipes are useful when gas it not 
available. Fig. 18 illustrates this form of blow-pipe. Wood 
or denatured alcohol may be used, and a needle-pointed 
flame of remarkably high temperature will result. The 
double-jet construction of the burner generates the maximum 
degree of heat from the fuel, over 1600° C. (3000° F.). The 
flame is perfectly clean and non-oxidizing. The burner is 
swiveled so that it can be turned in any position. 

Gasoline. — In Fig. 19 we have a very convenient form of 
gasoline lamp for melting base metals. The stand may be 
used for holding the melting pot or other objects to be heated. 
Fig. 20 represents the familiar form of gasoline torch, fitted 
with a holder so that it may also be used for heating objects. 
The torch may be released from the stand and also be used 
for soldering purposes. 

Gas Burner, etc. — The familiar Bunsen burner will not 
require a description; however, a word or two in regard to 
the nature of the flame may not be amiss. A flame may be 
considered a mass of highly heated gases, undergoing rapid 
combustion. The Bunsen-burner flame is made up of three 
cones: (1) consisting of a mixture of combustible gases; 
(2) consisting of gases in which combustion is starting; 
because of the nature of this cone, being low in oxygen, it is 
called the reducing flame, abbreviated R. F.; (3) consisting 
of gases in which combustion is completed; there is sufficient 
oxygen present to completely oxidize the combustible gases. 
This flame is called the oxidizing flame (O. F.). 



80 



METALLURGICAL APPARATUS 



To increase the rate of combustion, which would result in 
also raising the temperature of the flame, a blast is made use 




Fig. 18— Blow-pipe for alcohol. 
(Central Scientific Company.) 




Fig. 19. — Blast lamp, gasoline, 
"Dangler's lamp." (Central 

Scientific Company.) 




Fig. 20. — Adjustable laboratory blast lamp, fitted with adjustable stand 
and tripod. (Central Scientific Company.) 



HEATING DEVICES 



81 



of. The blow-pipe in its simplest form is used by a blast 
from the mouth. The large end of the instrument is held 
between the lips and the small end toward the flame. The 
blast should not be sustained by the respiratory organs, but, 
in order that an unbroken current may be kept up, the mouth 
should be filled with air, to be forced through the blow-pipe 




by the muscles of the cheeks. While these are forcing the 
air through the blow-pipe, the connection between the chest 
and the cavity of the mouth should be closed by the palate, 
which thus performs the part of a yalve. The beginner is 
liable to fall into the error of not closing the connection 
between the chest and the mouth at the proper instant, so as 
to obtain the force necessary to propel the air through the 
blow-pipe from the lungs. To avoid tiring the muscles of the 



Fig. 22 



lips by continual blowing, the trumpet mouth-piece has been 
recommended (Figs. 21 and 22). This is merely pressed 
against the open mouth, and an uninterrupted blast may 
be kept up for a long time without causing fatigue of the 
orbicularis oris, since that muscle takes but a passing part 
in the operation. 
6 



82 



METALLURGICAL APPARATUS 



The blow-pipe should be constructed of either brass or 
German silver, as these alloys are but poor conductors of 
heat. 

A long-continued and steady flame maintained by the 
mouth blow-pipe is apt to cause a disturbance in the flame 
from the collection of moisture in the tube, which is liable 




Fig. 23 

to be expelled by the pressure of the air. To avoid this, a 
hollow chamber is constructed about midway in the instru- 
ment. Fig. 23 illustrates another type of blow-pipe, usually 
connected with a bellows for the furnishing of the air blast; 




Fig. 24 



Fig. 24 is the usual form of bellows used in dental metal- 
lurgical operations. 

Compressed air, furnished by electric switchboards, is the 
common form of blast that is being used at the present time, 
and the up-to-date office buildings are also prepared to furnish 
compressed air to their patrons. 



HEATING DEVICES 83 

When a small quantity of gold or silver is to be melted by 
means of the blow-pipe, it is usually performed upon a support 
of charcoal. A good solid cylindrical piece of thoroughly 
charred pine coal should be selected, and divided into two 
equal halves by a vertical cut with a saw. Upon the end of 
one-half, a depression should be cut for the reception of the 
metal to be melted. On the flat side of the other half, 
extending to the end, the ingot mold should be carved, of 
size and shape governed by the requirements of the case. 
The two halves should then be brought together and secured 
by a piece of iron or copper wire, when they will be found to 
practically combine the requirements of crucible and ingot 
mold. The depression in which the metal is to be melted 
and the mold or receptacle should be connected by means 
of a gutter or groove. The flame is now 
directed upon the metal, and when thor- 
oughly fluid, the charcoal is tilted so that 
the fused metal will run into the mold 
prepared for it in the opposite half of the 
charcoal. This is probably the simplest 
form of apparatus by which small quantities 
of metal can be melted, and is often employed Fig. 25 

in the dental laboratory and by jewellers. 

Fletcher has devised an apparatus embodying the same 
general principles as the one just described for quickly 
obtaining ingots of gold and silver without the use of a 
furnace. It is shown in the accompanying diagram (Fig. 
25); A, representing a crucible of molded carbon, supported 
in position by an iron side-plate; C, the ingot mold; D, 
clamp, holding ingot mold and crucible in position; B, 
cast-iron stand upon which the latter swivels. The metal 
to be melted is placed in the crucible A, and the flame of 
the blow-pipe directed upon it until it is perfectly fused. 
The waste heat serves to make the ingot mold hot. The 
whole is tilted over by means of the upright handle at the 
back of the mold. A sound ingot may be obtained by the 
use of this simple little apparatus in a very few minutes. 
Simple contrivances of this kind are, however, not applicable 




84 



METALLURGICAL APPARATUS 



to melting operations involving quantities exceeding one 
ounce. In such cases it is better to employ a crucible and 
any stove or furnace in which the temperature can be raised 
sufficiently. This may be accomplished in an ordinary cook- 
ing stove, a blacksmith's forge, or a small fire-clay furnace, 
by the use of anthracite coal, coke, or charcoal. 

Fletcher Furnace. — By far the most convenient, compact, 
and effective furnace for melting from 1 to 10 ounces of 
gold, which has ever been used, is the crucible furnace (Fig. 
26), invented by Mr. Fletcher, which can be obtained at the 
dental depots. The furnace is perfectly adapted to the wants 
of the mechanical dentist. It is composed of a substance 




Fig. 26 



resembling fire-clay, but much lighter in weight, and said to 
possess only one-tenth its conducting power for heat. 

The furnace consists of a simple pot for holding the 
crucible, with a lid and a blow-pipe, all mounted on a suitable 
cast-iron base. As compared with the ordinary gas furnace 
it appears almost a toy, owing to its great simplicity. The 
casing holds the heat so perfectly that the most refractory 
substances can be fused with ease, using a common foot- 
blower. Half a pound of cast-iron requires from seven to 
twelve minutes for perfect fusion, the time depending on the 
gas supply and the pressure of air from the blower. The 
power which can be obtained is far beyond that required 
for most purposes, and is limited only by the fusibility of the 



HEATING DEVICES 



85 



crucible and casing. The crucible will hold about ten ounces 
of gold. An ordinary gas supply-pipe of ^ or | inch diam- 
eter will work it efficiently. It requires a much smaller supply 
of gas than any other furnace known; about 10 cubic feet 
per hour is sufficient for most purposes. Crucibles must 
not exceed 2J x 2 inches. Any common blow-pipe bellows 
will work the furnace satisfactorily, except for very high 
temperatures (fusion of steel, etc.), for which a very heavy 
pressure of air is necessary. In size, it is but four inches in 
diameter by three in height. The author has used one in 
his laboratory for the purpose of melting gold and silver 
and for general metallurgical experiments for several years 




Fig. 27 



with the greatest satisfaction; he has also found it to be 
most admirably adapted to class demonstration, for which 
purpose, as a means of illustrating his lectures on metallurgy, 
he has had frequent opportunities to use it. 

A modification of the apparatus has been made, adapting 
it to the use of refined petroleum instead of gas as a fuel, 
and thus rendering it of more general utility (see Fig. 27). 
Thus improved, it is said to be in no way inferior in efficiency 
to the gas furnace. The burner of this furnace is constructed 
upon the principle of an atomizer, which, of course, dispenses 
with a wick; it is supplied with a device for regulating the 
supply of oil, which is operated by the milled nut (marked A) 
shown on the top of the reservoir in the cut, and for the supply 



86 



METALLURGICAL APPARATUS 



of an annular jet of air, which is regulated by turning the 
sleeve (marked B). This burner is so arranged that in case 
any obstruction should occur it can be taken apart and 
cleaned by separating the burner from the reservoir, which is 
accomplished by loosening the small screws, drawing out 
the oil-tube, taking off the sleeve B, and removing the inside 
tube. 

These furnaces are so constructed that they may be used 
for either gas or petroleum, the lamp being fitted for adjust- 
ment in place of the gas-burner, so that the same apparatus 
may be used for either. The blast is obtained by means of 
the foot-blower shown in Fig. 24, which is connected with 
the furnace by means of India-rubber tubing, as seen in 
Fig. 27. 




Fig. 28 



Muffle Furnace. — Brown's assay furnace (Fig. 28) illus- 
trates this form of furnace; in it coke is used as a fuel. 
The older furnaces used in continuous gum work were of 
this type. The muffle used is of a refractory material and 
during the heating process the metals do not come in contact 
with the products of combustion. If an alloy of gold and 
lead is placed in the muffle in a small dish composed of bone 



HEATING DEVICES 87 

ash, the lead will be oxidized, leaving the gold as a bead. 
This process is called cupellation; the bone ash dish is the 
cupel. 

The electric muffle furnace consists of a muffle wrapped 
with platinum wire of about 28-gauge, and then covered with 
a mixture of refractory materials, such as fire-clay. The 
muffle is then put into position in the outside casing, which 
differs in the various makes of furnaces. The platinum- wire 




Fig. 29 

wrapping leads to binding posts. Then from the binding 
posts it passes to some form of a resistance coil which regu- 
lates the amount of current passing through the furnace. 
The resistance coil or rheostat gives us control of the tem- 
perature. Hoskins' furnace is a good illustration of a furnace 
in which electricity is made use of for heating purposes. 
Fig. 29 illustrates this type of furnace. Chromel, a nickel- 
chromium alloy, is used instead of platinum. 
The electric furnaces used in porcelain work, of which 



88 



METALLURGICAL APPARATUS 



there are many types in use, as a rule contain platinum wire 
and serve to illustrate an electric muffle furnace. 

Refractory Materials. — Refractory agents are those that 
can withstand the agency of heat without destruction. The 
ideal refractory material should not decompose or crack 
upon sudden changes of temperature, nor be attacked by the 
metal or flux used during the heating process. They are 
used: (a) In the construction of furnaces. Example: fire-clay. 
(6) To construct crucibles or other receptacles for melting 
metals. Examples: fire-clay, graphite, charcoal, asbestos, 
etc. (c) To line furnaces and crucibles. Examples: oxide 
of iron, magnesium oxide, etc. (d) To act as a support for 
metallic pieces during soldering or casting. Examples: 
investing compounds of various compositions. 





Fig. 30 



Fig. 31 



Crucibles. — The term " crucible" is applied to a chemist's 
melting pot (Figs. 30 and 31), made of earthenware or other 
material, and so-called from the superstitious habit of the 
alchemists of marking such vessels with the sign of the cross. 
The term is now generally understood as designating vessels 
in which metals are melted in furnaces at high temperatures. 
A crucible should possess the power of resisting high tem- 
peratures without fusing or softening. It should also be 
capable of retaining sufficient strength, when hot, to prevent 
its crumbling or breaking when grasped by the tongs. Lastly, 
it should not crack either in heating or cooling. 

For the purpose of melting metals, crucibles are made of 



HEATING DEVICES 89 

clay with admixture of silica, burnt clay, graphite, or other 
infusible material. For the fusing of platinum, which requires 
the intense heat of the oxhydrogen flame, they are formed of 
lime. For use in the dental laboratory, graphite crucibles, 
which can be obtained at the dental depots, will be found to 
answer every purpose, and they are thoroughly reliable in 
strength and durability. They range in size from 2 to 4 
inches high. When the quantity of metal to be melted is 
very small, say a half-^unce of gold, the smallest-sized 
Hessian crucible may be used in the small Fletcher apparatus. 
Crucibles suitable for melting platinum or iridium are formed 
of two blocks of lime, each block having a concavity or 
excavation, so that when the two pieces are placed together 
the center is hollow; it is thus designed to hold the scraps of 
platinum to be melted. The lower block is also arranged 
with a groove and lip, so that when the metal becomes fluid 
it may be poured into a suitable ingot mold by inverting 
the crucible. The compound flame is introduced by tubes 
passing through the center of the upper block of lime forming 
the cover. 

Before melting any considerable quantity of gold, the 
crucible should be tested, particularly if the melting operation 
is to be performed in an ordinary coal stove, where a defective 
crucible might be the means of a considerable loss. A small 
amount of borax should be placed in the vessel, which should 
then be exposed to a high temperature. Should it not be 
perfect, the borax glass will run through and glaze the surface 
on the outside. If the crucible is found to be impervious 
it should be so inverted, while yet hot, that the borax glass 
may cover the surface of the lip or groove out of which the 
melted metal is to be poured. This facilitates the pouring 
and prevents any portion of the metal from adhering to the 
side of the crucible. 

Scorifiers (Fig. 32). — Scorifiers are small dishes from 
2 to 3 inches in diameter and about 1 inch deep. They are 
made of a refractory fire-clay, like crucibles, and should not 
be too deep, as the object is to expose the largest possible 
surface of molten lead to the air current. 



90 



METALLURGICAL APPARATUS 



Roasting Dishes. — Roasting dishes are similar to scoriflers, 
except that they are a little more shallow and much wider. 

Cupels. — Cupels, as the name indicates, are small, cup-like 
receptacles. They are made of bone-ash obtained by burning 
the bones of horses and cattle. It is customary to mix the 





Fig. 3i 



Fig. 33 



pulverized bone-ash with 1.5 to 2 per cent, of fire-clay and 
with a little water, just enough to make it stick together 
without making it appear wet. This is then packed into a 
suitable mold and compressed by means of a die. The 
cupel is then removed from the mold and allowed to become 




Fig. 34 



thoroughly dry in the air, and finally calcined to expel all 
moisture and to decompose any organic matter which might 
be present in the form of splinters of wood, small pieces of 
paper or other impurities. If this calcinating were not done, 
the gases arising when first heated would cause a spattering 



HEATING DEVICES 



91 



of the molten lead and a consequent loss of noble metal in 
the assay. 

Scorification Molds (Fig. 33) .—These are used for pouring 
the assay charge. The conical shape is preferable to the 
old-fashioned flat style. 




Ingot Molds. — Ingot molds are constructed of various 
substances. For the reception of platinum melted with the 



92 



METALLURGICAL APPARATUS 



oxyhydrogen blow-pipe they are formed of lime or coke; for 
gold and silver they are commonly made of cast-iron, about 
2 inches square and from | to ^ inch in thickness (Fig. 34), 
with slightly concave inner surfaces, as the shrinkage of the 
ingot is greatest at the center. Ingot molds formed of 
soap-stones are also employed. The ingot mold should 
be heated before pouring. 



^BRo 




Fig. 36 



The Rolling Mill. — Rolling or laminating is accomplished 
by repeatedly passing the metallic ingot between cylindrical 
steel rollers from 3 to 4 inches in width. These are so arranged 
that by means of screws, they are capable of being brought 
closer together every time the gold is passed through (Fig. 
35). The proper degree of attenuation is determined by the 
gauge-plate (Fig. 36). 

Draw-plate (Fig. 37). — Gold or silver is made into wire by 
means of the draw-plate — an oblong piece of steel provided 
with a number of gradually diminishing holes enlarged on the 
side where the gold enters. The gold to be drawn through 
may be prepared in a cylindrical shape by melting and 



INSTRUMENTS AND METHODS 93 

pouring into an ingot mold provided with a chamber for 
the purpose (some ingot molds are so constructed). The 
end of the rod should be filed so as to readily enter the draw- 
plate, which must be firmly screwed in a vise. The gold is 
then, by means of a pair of strong pliers, drawn through 
the different holes of the draw-plates consecutively until the 
desired size is reached. At the beginning of the operation 
it will require frequent annealing. 



GARANTIE 
Fig. 37 

INSTRUMENTS AND METHODS OF DETERMINING 

PHYSICAL PROPERTIES OF METALLIC 

SUBSTANCES. 

Specific Gravity. — The chemical balance (Fig. 38) is used 
in weighing the object in air, and then a small platform is 
placed over the pan of the balance; a beaker of water is then 
placed on the platform; the difference in weight in air and 
in water is the weight of an equal volume of water. The 
specific gravity of a substance will then be represented by 
the following: 

Sp. gr. = ^j — ™, when W is the weight in air, and W 

equals weight in water. 

Temperature. — Mercury thermometers are used for tem- 
peratures as high as 360° C; above this temperature mercury 
boils, and some other device must be used. 

Low fusing metals or alloys may be fused in a "Jena" 
glass flask, placed upon a sand-bath to insure uniform 
heating of the flask. Care must be taken not to let the 
thermometer touch the sides of the glass, or a false reading 
of the temperature will result. Crucibles or hard test-tubes 



94 



METALLURGICAL APPARATUS 



may also be used instead of the Jena flask. For high tem- 
peratures, pyrometers must be used. The name pyrometer 
is given to those instruments for measuring temperatures so 
high that mercurial thermometers could not be used. The 
three principles upon which pyrometers are constructed are: 

1. The expansion of gases and vapors. 

2. The specific heat of solids. 

3. The electric properties of bodies. 




Fig. 38 

Pyrometers of the third group are the only ones that need 
to be described; information on the first two classes may be 
found in any book on physics. 

If two metals are soldered together, their extremities 
joined in a metallic circuit and the junction between them 
heated, an electric current is produced. This was called a 
thermo-electric current. The thermo-electric motive force 
is dependent upon the temperature. A thermojunction of 



INSTRUMENTS AND METHODS 



95 



palladium and platinum wires was used by Becquerel for 
measuring the temperature of a furnace. The wires were 
firmly tied together by platinum wire for a distance of 1 cm. 
at one end. This junction was placed in the region the 
temperature of which was required; the wires being protected 
by a porcelain tube, and their outer ends soldered to copper 
wires in circuit with a sensitive galvanometer. The junction 
is placed in a vessel of melting ice so that the two metals 
being at the same temperature, could not give rise to any 
thermo (E. M. F.). The galvanometer deflection is pro- 




Fig. 39 



portional to the temperature of the furnace and the instru- 
ment is first standardized by being placed into various 
substances at their known melting point. This explains the 
principle of the pyrometer of the third class, as originally 
worked out. In Fig. 39 we have a pyrometer consisting of a 
thermo couple and a temperature indicator. The fusing 
point of brass, bronze, lead, and zinc may be readily deter- 
mined with this instrument. The maker guarantees this 
instrument accurate up to a temperature of 1200° C. and 
may be used to indicate a temperature as high as 1400° C. 



96 



METALLURGICAL APPARATUS 



Linear Expansion. — Linear expansion is determined by 
the expansion of a rod of the metal during a given range of 
temperature. Fig. 40 represents an apparatus for determin- 
ing the linear expansion of a bar of metal. The apparatus 
consists of a water jacket, a binding screw, place for a 
thermometer; at the opposite end to the binding post there 
is a lever attached to a pointer; also a graduated scale or 
dial to record results. The metallic rod is placed in position 
within the steam jacket, and the set screw is regulated; the 
thermometer is next set into place. Cold water is run 
through the water jacket and the temperature reduced to 
zero degrees if possible; in the most exact determinations 
with more complicated apparatus, this is necessary. The 




Fig. 40 

length of the rod at zero is fixed by means of the set screw 
and the latter is regulated so that the pointer stands at zero 
on the scale. The temperature of the water is gradually 
changed, and finally steam is passed through the water 
jacket until the thermometer registers 100°. The dial, which 
registers the elongation produced, is read and the amount of 
expansion per degree per cubic centimeter is calculated. 

Conductivity of Heat. — Two similar bars of metal are 
placed end to end and heat applied. The temperature of the 
bars in different places is measured by applying the junction 
of a thermo-electric couple. Wiedeman and Franz made use 
of this method of determining the conductivity in the 
following way: The metal bars were made as regular as 
possible and were silver-plated and polished so as to have the 
same radiating power, one of the ends was heated to 100°, 



INSTRUMENTS AND METHODS 97 

the rest of the bar being surrounded by air at a constant 
temperature. The results of their experiments are the figures 
given in Chapter III. 

Specific Heat. — The specific heat of substances may be 
determined in any of the following ways: 
I. Method of mixtures. 
II. Method of melting ice. 

III. That of cooling. 

IV. By the steam calorimeter. 

I. Method of Mixtures. — By this method the specific heats 
of the metals may be determined in the following manner: 
The substance is weighed and raised to a known temperature 
by keeping it for some time in a place heated by steam ; it is 
then immersed in a mass of cold water, the weight and tem- 
perature of which is known. From the rise of temperature 
of the water after mixture the specific heat of the body is 
determined. If a kilogram of water and a kilogram of mercury 
be each heated to 100° and then poured into a separate 
kilogram of water at 0°, in the first case the water will raise 
the temperature of the water to 50°, while the mercury will 
raise the temperature of water 3.2°. While the water in 
cooling has raised the temperature of an equal weight of water 
from 0° to 50°, the amount of heat in a kilogram of mercury 
at 100° has only raised the temperature of an equal weight 
of water from 0° to 3.2° and in doing so has itself become 
lowered in temperature, 100— 3.2 = 96.8°. The amount of heat 
contained, therefore, in equal weights of water and mercury 
at the same temperature as shown by these figures, is as : 

50 3.2 1 

i5 : 9678 =1: 35° r0 - 33 - 

II. Method of Melting Ice. — This method was devised by 
Black, the discoverer of specific heat. A cavity is made in a 
piece of ice to receive the metal to be tested. An ice covering 
is then made to fit tightly over the cavity to prevent a loss of 
heat from this source. 

The metal is weighed and heated to a given temperature, 
the cavity in the ice is thoroughly dried — the metal is then 
7 



98 METALLURGICAL APPARATUS 

introduced and allowed to remain until it reached the tem- 
perature of the ice (0°). The water from the melted ice is 
collected upon weighed blotting paper or a sponge and again 
weighed to ascertain the quantity of ice melted. The specific 
heat is then calculated as follows : 

_ Latent heat of ice (80 cal.) X weight water. 

Weight of metal X temperature difference of metal. 

When ice passes from the solid to the liquid state it takes up 
80 calories of heat (as energy of the molecule) and when the 
weight of water as determined by this experiment is multiplied 
by 80, the product represents the number of calories of heat 
which is given up by the metal in passing through the range of 
temperature. If this quantity be divided by the weight of the 
metal times the number of degrees through which the metal 
has passed, the result will represent the quantity of heat per 
gram of weight which the metal possessed as compared with 
water (specific heat) . 

III. By Cooling. — This method is not used in determining 
the specific heat of metals or other solids ; however, it is of 
service in determinations upon liquids. The method is based 
upon the fact that substances possessing different specific 
heats will have their temperatures reduced at a different rate 
in succeeding units of time. By accurately measuring the 
rate of fall in temperature, the specific heats of liquids may be 
determined. 

IV. Steam Calorimeter. — A known weight of a substance, 
at a known temperature is placed in a vessel containing steam 
and again weighed ; from the weight of condensed steam upon 
the object, the quantity of heat which has been required to 
raise the substance to the given temperature of the vessel is 
estimated. The latent heat of water being known (607 cal.), 
then the specific heat may be obtained by the following 
formula : 

wt. condensed water X 607 cal. 
Sp - heat = wt. substance X (t 1 — t°) ' 

In this equation t° represents the first temperature of the 
object and t 1 , the temperature to which the object has been 
raised during the condensation of the steam. 



INSTRUMENTS AND METHODS 99 

Measure of the Quantity of Heat. — The quantity of heat 
disengaged during chemical action is measured by means 
of the calorimeter. Oxidation is the principal chemical 
action used in obtaining quantities of heat, as in the burning 
of the various fuels. An instrument is so devised that the 
heat given off is taken up by a known weight of water, and 
from this the caloric value is calculated according to the 
standard established for the calorie, as has been elsewhere 
stated in this text. The following list gives the heat in 
calories, disengaged by a gram of each of the substances 
while burning in oxygen: 

Hydrogen . . . 34,462 Coke 7000 

Petroleum . . . 11,000 Carbon monoxide . 2400 

Anthracite . . . 8,460 

Conductivity of Electricity.— Conductivity of electricity is 
a term used to refer to a specific property of a material 
which conducts an electric current through a unit of length 
and cross-section. The physical condition of a metal and 
also the temperature at which the determination is made 
both have an influence upon the conductivity. The table 
in this text is a comparative one, using the conductivity of 
silver as 1000. By dividing the absolute unit of resistance 
represented in microhms of silver by the figure representing 
the resistance of some other material represented in the same 
unit, and then multiplying by 1000 the figures used in the 
table were obtained. 

Hardness. — For ordinary purposes the table of comparative 
hardness may be used. In this table we have ten degrees of 
hardness; No. 10 will scratch any substance in the scale, 
while No. 9 will scratch all those below it, but will in turn 
be scratched by No. 10. The following is the table of com- 
parative hardness: 

1. Talc, . 6. Orthoclase, 

2. Gypsum, 7. Quartz, 

3. Calcite, 8. Topaz, 

4. Fluorite, 9. Sapphire, 

5. Apatite, 10. Diamond. 
Corborundum ranks between No. 9 and No, 10, 



100 METALLURGICAL APPARATUS 

The table of hardness of metals is as follows : 

Lead, Zinc, 

Tin, Copper, 

Aluminum, Soft iron, 

Gold, Mild steel, 

Silver, Hard cast iron, 

Platinum, Hardened steel. 

Hardness of a body has no relation to its resistance to 
compression. Glass and the diamond are much harder than 
wood, but the latter offers far greater resistance to the blow 
of a hammer. 

Tenacity. — For measuring the tensile strength of wires, 
Fig. 41 represents one of the various forms of devices. The 



iill^ffi 




Fig. 41 

wire of definite gauge is placed in the machine and force is 
applied by means of the lever. The machine is fitted with a 
spring balance for recording the amount of force applied. 

Malleability and Ductility. — The figures given are only 
approximate as there is no means of standardizing these 
physical properties. 

SPECIAL METALLURGICAL OPERATIONS. 

Study of an Alloy. — The following is a brief outline as to 
the method of studying an alloy: 

Thermic Analysis. — The metals are alloyed and allowed 
to cool slowly; the time consumed in the fall of temperature 
is carefully noted, and recorded. By this means the forma- 
tion of eutectics may be determined by the arrest in the fall 



Seconds. 


Centigrade. 





350° 


10 


328 


20 


307 


30 


287 


40 


267 


50 


250 


60 


238 


70 


227 


80 


215 



SPECIAL METALLURGICAL OPERATIONS 101 

of temperature. To illustrate: An alloy is heated to, say, 
350° and the temperature recorded every ten seconds. 1 

Seconds. Centigrade. 

90 202° 

100 188 

110 184 

120 180 

130 180 

140 180 

150 180 

160 169 

170 159 

The conclusion drawn from the above chart shows: (1) 
A primary retardation of cooling, lasting from 250° C. to 
180° C, and during this interval a primary crystallization 
has taken place; (2) The temperature remains stationary 
for thirty seconds at 180°, indicating a second crystallization 
at this point. The above is an alloy of lead 65 per cent, and 
tin 35 per cent. The arrest of the temperature upon cooling 
is due to crystal formation; the latent heat given off during 
solidification causes this arrest. 

Microscopic Examination. — The metallic substance is highly 
polished and then etched with some suitable acid. Nitric 
(dilute or concentrated), picric, or hydrochloric acids, may be 
used. The object of etching is that it brings out the crystal 
formation so that it may be more readily seen through the 
lens. The microscope for this purpose is so constructed 
that opaque objects may be readily seen; it is fitted with a 
mirror, so situated that light is reflected to the surface of the 
metal, which is seen through the eye-piece. The physical 
properties are studied by the methods already described in 
this chapter, and finally a quantitative chemical analysis 
is made to determine the composition; this last step is very 
important, due to the fact that there may be a change in the 
proportions of the metals present in an alloy, due to oxidation 
during alloying. 

Soldering. — Soldering must also, to a certain extent, be 
regarded as coming under the general head of melting opera- 

1 Fenchel. 



102 METALLURGICAL APPARATUS 

tions, since it refers to the union of two or more pieces of 
metal by means of a more fusible alloy. The conditions of 
successful soldering are: (1) Contact of the two pieces to be 
united. (2) A clean metallic surface over which the solder 
is to flow. (3) A freely flowing solder. (4) Proper amount 
and distribution of heat. 

Contact of the pieces to be united is of the greatest impor- 
tance. If, for example, the object to be soldered be an arti- 
ficial denture, it is an indispensable requirement that the 
backings be quite or very nearly in contact with the plate, 
and, if gum teeth be .used, that each backing touch its 
neighbor. If, however, any defects of this character are 
found to exist after the teeth have been invested, they should 
be remedied by filling such spaces or crevices with small 
pieces of gold or silver, as the case may be, thus rendering 
the continuity of the parts complete. By the observance of 
this precaution much of the vexation in soldering experienced 
by beginners may be avoided, and when the other conditions 
named have been observed, the operation becomes exceed- 
ingly simple. Solder runs freely by the force of capillary 
attraction between two closely fitting surfaces, just as water 
will be drawn against gravity between two panes of glass in 
close contact. The difficulties of soldering are mainly due to a 
violation of one or more of the rules herein given. Cleanliness 
should always be strictly observed in soldering operations. 
The parts to be united should present bright and clean sur- 
faces. Darkening by oxidation will always occur when gold 
or silver, which has been alloyed with copper or brass, is 
heated to redness. A weak solution of sulphuric acid and 
water, slightly heated, will quickly remove discoloration 
resulting from this cause; or the borax employed as a flux in 
soldering operations will effect the same result by dissolving 
the oxide which forms on the surface, while it also protects 
from further oxidation by excluding the oxygen of the 
atmosphere. The surfaces to be soldered should be carefully 
protected from any contact with plaster of Paris, as there is 
no substance used in the dental laboratory more likely to retard 
the union of the parts and impair the final result than this. 



SPECIAL METALLURGICAL OPERATIONS 103 

A solder to be employed in dental mechanics should 
possess the quality of flowing freely, and be as high in grade 
as the attainment of that property will permit, so that it 
will sufficiently resist the action of the fluids of the mouth. 
It should also approximate as nearly as possible the color 
of the plate upon which it is used. If the first condition, 
referring to the contact of the plates to be united, be observed, 
the quantity of solder required to effect continuity will be 
reduced to the minimum ; and thus we shall have the smallest 
possible portion of the alloy exposed to the action of the fluids 
of the mouth, while we at the same time avoid the danger of 
fracture of the teeth by the contraction in cooling of an 
inordinate quantity of solder. 

The application and management of the heat in the 
operation of soldering are matters requiring both care and 
judgment. The temperature should at first be raised very 
gradually, in order that pieces of solder may not be thrown 
off or displaced by the puffing-up incident to the calcination 
of the borax. Both parts to be united should be equally 
heated; therefore the heat should be so applied in the case 
of an artificial denture as to raise the teeth and plate to 
an equal temperature; otherwise, should the plate become 
sufficiently hot while the teeth remain comparatively cool 
(a condition likely to occur unless the fuel has been built 
up around the outside of the investment covering the teeth), 
the solder, when the flame of the blow-pipe is directed upon 
it, will flow upon and adhere to the plate. In other words, 
it will manifest a preference for the hottest portion. The 
failure to effect an equal distribution of heat preparatory to 
soldering is often the cause of much vexation and delay. For 
example, in the process of uniting a rim to a plate by soldering, 
the rim, being so much smaller than the plate, will be more 
quickly heated, in which event the solder will fuse and flow 
upon the rim, and the attempt to unite it to the plate will 
not be successful. But to avoid such a result, the flame of 
the blow-pipe should, as a preliminary step, be directed 
exclusively upon the latter, and union of the rim and plate 
can hardly fail to take place. 



104 



METALLURGICAL APPARATUS 



Supports. — In melting small quantities of gold or silver, 
or in soldering with the blow-pipe flame, it is necessary to 
perform these operations upon a support made of some suit- 
able body, such as charcoal, coke, pumice-stone, or asbestos 
and plaster, charcoal and plaster, etc. 

Autogenous Soldering. — Autogenous soldering is a sweat- 
ing process in which a lower fusing alloy is not used. The 
metallic parts are brought to intimate contact and the pieces 
heated until the metals fuse upon their surfaces, and thus form 
a joint. Gold, by using great care, may be soldered in this 
manner. Lead surfaces are also frequently united by autog- 
enous soldering as in the lead chambers of the sulphuric 
acid industry. 





Fig. 42 



Welding. — Within the last few years welding, or as it is 
called autogenous welding, by the use of oxyacetylene gas, 
has come into use. Extremely high temperatures can be 
obtained by this mixture of gases, and with the proper form of 
blow-pipe very neat welding may be accomplished. Another 
very interesting fact is that a blow-pipe can give a flame 
that may be used for cutting metals. The author has seen 
a piece of steel § inch thick and 3 feet in breadth cut in a 
very few minutes by this form of device. Fig. 42 shows 
a cast-iron gear welded through hub and rim. Large station- 



SPECIAL METALLURGICAL OPERATIONS 105 

ary machines may be welded without moving them from 
their positions, which would necessitate a great amount of 
expense and also in some cases mean the shutting down of the 
manufacturing plant. The author has seen a weld made of a 
piece of iron pipe to which was welded an inner tube of copper 
and then, to this, an aluminum cylinder was welded to the 
copper. 



CHAPTER VI. 

COMBINATION OF METALS WITH THE NON- 
METALLIC ELEMENTS. 

The metallic elements form chemical compounds with the 
non-metals. The substances formed in no way resemble the 
metals entering into their compositions. These compounds 
are formed in three ways: 

(a) By inorganic nature, giving rise to those substances 
known as minerals. 

(6) In the dry way, due to the agency of heat. 

(c) In the wet way. 

The factors at work in the formation of minerals are: 
Heat as represented by those substances classified from a 
geological point of view as belonging to the " igneous period;" 
water, as in the formation of the so-called sedimentary 
deposits. At the present time there is a tendency of the 
natural elements to break down the complex compounds 
into simpler substances. The breaking up of silicates into 
carbonates, with the liberation of silicon dioxide, represents 
this form of phenomenon. The decomposition of feldspar 
into kaolin and silica is of interest to the dental profession, 
as all of these materials are used in porcelain bodies. This 
reaction may be represented as follows: 

Na 2 1 

A1 2 3 (bl ° 2)x + C ° 2 + H *° - { k 2C o 3 + Fe 2 3 \ Si0 2 +Si0 2 . 
Fe 2 3 J [H2O j Silica. 

Kaolin . 

Metamorphic Rocks. — Metamorphic rocks, those formed by 
an alteration of heat, moisture and pressure, are of especial 
interest, as the most valuable minerals of the metals are 
found in metamorphic formations. 



SULPHIDES 107 

Metallic compounds formed in the dry way due to the 
agency of heat, such as sulphides, silicates, oxides, borates, 
chlorides, sulphates, are among the compounds commonly 
met with. 

Metallic compounds are formed in the wet way by the 
action of acids upon a metal ; this is one of the most common 
methods used. 

Halogens. — The halogen elements include chlorine, 
bromine, iodine, and fluorine. Nearly all of the metals 
combine directly with the halogens. The power of aqua 
regia 1 to dissolve the noble metals depends upon the liberation 
of chlorine in the nascent state. The compounds of these 
elements and the metallic elements, may be formed by the 
following reactions 

(a) A metal treated with the hydrogen acids of the 
halogen, i. e.\ 

HC1, HBr, HI, HF. 

(b) Oxides, carbonates, and sulphites treated in the same 
manner as (a). 

(c) By double decomposition in solution. 

The following reactions illustrate the different methods: 

(a) Zn + 2HC1 = ZnCl 2 + H 2 . 

f ZnO + 2HC1 = ZnClo + H 2 0. 

(6) \ ZnC0 3 + 2HC1 = ZnCl 2 + C0 2 + H 2 0. 

[ ZnS0 3 + 2HC1 = ZnCl 2 + S0 2 +- H 2 0. 

(c) AgN0 3 + NaCl = AgCl + NaN0 3 

Most of the halogen salts of the metals are soluble in water; 
the exceptions are lead, silver and mercurous salts. Sodium 
chloride, silver chloride, silver iodide, silver bromide, cryolite 
(sodium and aluminum fluoride) are some of the natural 
occurring compounds of the halogen elements and the metals. 

Sulphides. — Sulphides may be formed by heating a metal 
with sulphur; by passing hydrogen sulphide through a 
solution containing a metallic salt; by the reduction of 
compounds containing the metal in combination with sulphur 

1 Aqua regia, i. e., three volumes hydrochloric with one volume of nitric 
acid. 



108 COMBINATION OF METALS 

and oxygen (sulphates). To illustrate: iron when heated 
with sulphur forms iron sulphide— FeS. 

Fe + S + heat - FeS. 

Silver combines readily with sulphur; and the tarnishing of 
silver when exposed to the atmosphere, is due to the formation 
of the sulphide. 

When hydrogen sulphide is passed through a solution of a 
metallic salt, a sulphide of the metal is formed. The separa- 
tion of metals in qualitative analysis is based upon the 
solubility of these sulphides. The sulphides of the alkali and 
alkali earth metals are soluble in water; iron, cobalt, nickel, 
manganese and zinc sulphide are soluble in acid solutions, 
while silver, lead, mercury, copper, cadmium, bismuth, 
arsenic, antimony, tin, gold and the platinum groups are 
insoluble in acid or alkaline solution. Chromium or aluminum 
do not form sulphides in the tvet way. 

Sulphates when heated with carbon, are reduced to 
sulphides, as the following reaction will show: 

Na 2 S0 4 + 2C = Na 2 S + 2C0 2 . 

The natural occurring sulphides generally have a metallic 
luster, as in the case of iron pyrites, galena, stibnite, etc. 
Pyrites has frequently been mistaken for metallic gold and is 
called "fool's gold." The sulphides are one of the most 
frequent occurring metallic compounds of the metals and 
are only exceeded by the oxides. 

Oxides. — The oxides of the metals occur in nature, possibly 
as the result of decomposition of higher compounds of the 
metals. The noble metals, however, rarely if ever are found 
as oxides because they are so easily decomposed. Oxides 
are formed in any of the following ways: 

1. By heating a base metal in air or oxygen. 

2. By heating carbonates, nitrates and hydroxides. 
When base metals are heated in air they become oxidized. 

Sodium and potassium have such an affinity for oxygen 
that they must be preserved under petroleum. 

The kindling temperature of an element is the temperature 



REDUCTION OF METALLIC COMPOUNDS 109 

at which it unites with oxygen. This temperature varies 
with the different elements. Magnesium upon oxidation 
gives off a brilliant white light and is used as a flashlight 
powder in photography. Aluminum in the finely divided 
state combines with oxygen giving off so much heat that a, 
temperature of about 3000° C. is reached. The preparation 
of oxides may be facilitated by the presence of certain 
substances known as oxidizing agents. 

Superficial oxidation may occur by mere exposure to air 
at ordinary temperatures, particularly in the presence of 
moisture. It frequently happens, however, that metallic ob- 
jects thus superficially oxidized are protected by the newly 
formed oxide from further access of air so that oxidation 
can no longer go on; but upon the removal of the oxide from 
the surface oxidation will again occur. When the carbonates 
are heated, carbon dioxide and water are given off, leaving 
the oxide of the metal. The preparation of lime from lime- 
stone is a practical application of this method of preparation 
of oxides. Roasting, as has been stated, has for its object 
the heating of minerals, principally the carbonates, resulting 
in the formation of oxides. 

Nitrates, upon being heated, yield oxides of nitrogen, the 
oxide of the metal, and in some ckses, oxygen. 

Pb(N0 3 ) 2 + Heat = PbO + 2N0 2 + O. 

The hydroxides upon heating form oxides by the driving 
off of water. 

Cu(OH) 2 + Heat = CuO + H 2 0. 

REDUCTION OF METALLIC COMPOUNDS. 

The term " reduction," as used in metallurgy, refers to the 
different methods of separating a metal from its natural 
ores or from combination with any non-metallic element. 
In some cases this is effected by heat alone. For example, 
the noble metals are separated from oxygen by merely heat- 
ing to 315.5° C. Generally, however, the joint action of 



110 COMBINATION OF METALS 

heat and reagents, for which the non-metallic constituents 
of the compound have greater affinity, is required* 

The inventions of Eugene H. and Alfred H. Cowles, of 
Cleveland, Ohio, and of Graetzel, near Bremen, in Germany, 
have proved to be a most important advance in metallurgy. 
The essential features in the improvements made by these 
gentlemen, is the application of the intense heat of a current 
of electricity from a dynamo through a conductor of great 
resistance in the presence of carbon. Many of the most 
refractory ores, which have hitherto resisted all similar 
attempts, may be readily decomposed in these electric 
furnaces. By this means aluminum is now reduced from 
corundum. 1 

The metallic compounds, whether natural or artificial, 
are a class of bodies formed of dissimilar elements held 
together by the force of chemical affinity. This affinity 
varies much in different metals. Thus, gold possesses 
such feeble affinities that a dilute aqueous solution of gold 
chloride may be partially precipitated by mere exposure to 
light. The facility with which gold often passes from one 
element to another may be observed in the interesting 
process of manufacturing "shredded gold," 2 in which an 
acid solution of the trichloride is formed and slightly heated 
in a glass matrass; gum arabic or sugar dissolved in water 
is then added, when beautiful web-like masses of pure gold 
are seen to form in the liquid; but unless these are quickly 
removed by means of a glass spoon or dipper they will almost 
instantly dissolve and the gold again unite with the chlorine. 
Lead, tin, zinc, iron, and many other metals evince stronger 
affinities; hence they are not so readily reduced, and 
require, in addition to heat, the presence of other substances, 
such as coal, coke, charcoal, etc. In other words, it is neces- 
sary to expose them in contact with some reagent between 
which, and the non-metallic constituents of the compound, 
superior affinity exists, so that by union of these the metal 



1 See chapter on Aluminum. 

2 Lamm's shredded gold." 



REDUCTION OF METALLIC COMPOUNDS 111 

may be released. It may be said that all analytical opera- 
tions for the reduction of ores and the detection and estima- 
tion of unknown bodies are performed by taking advantage 
of the different degrees of chemical affinity. Thus, lead 
which has been overheated or subjected to frequent or long- 
continued meltings, becomes partially oxidized and covered 
with an earthy-looking mass consisting of semioxidized 
metal, formerly called the "calx." Further exposure to heat 
would simply have the effect of converting this into an oxide 
of a higher degree ; but if covered with finely broken charcoal, 
or other carbonaceous substance, 1 the latter will extract the 
oxygen, carbonic dioxide will be formed and evolved, while 
the metal will be restored to a free state. 

Chlorides. — With the exception of the chlorides of the 
metals of the alkalies and earths, all metallic chlorides are 
decomposed when heated in a current of hydrogen, hydro- 
chloric acid and the pure metal being the result. The 
chlorides of gold and platinum are decomposed by simple 
ignition. 

Argentic chlorides when heated on charcoal, under the 
flame of the blow-pipe, yields pure silver and emits an odor 
of hydrochloric acid. Placed in water acidulated with sul- 
phuric or hydrochloric acid, argentic chloride may be reduced 
by the addition of pieces of some easily oxidizable metal, 
such as zinc or iron, the rationale of the reaction being as 
follows: The zinc displaces the hydrogen of the H 2 S0 4 , 
zinc sulphate is formed, the liberated hydrogen unites with 
the chlorine to form hydrochloric acid, and pure silver 
remains. 

Concentrated sulphuric acid decomposes the chlorides and 
converts them into sulphates, the oxygen being supplied 
from the water present. Some chlorides may be decomposed 
by heating them with a metal which has more powerful 
basic properties. Thus, sodium when heated with aluminum 
or magnesium chloride will become sodium chloride, with 



1 In the dental laboratory beeswax is usually employed to deoxidize lead 
or zinc which has become thick and earthy by frequent meltings. 



112 COMBINATION OF METALS 

liberation of the magnesium or aluminum. Some chlorides 
are reduced by heating with a mixture of sodic carbonate 
and charcoal; other carbonaceous compounds, such as sodic 
or calcium carbonate, are frequently used. 

Sulphides. — Reduction of the sulphides in some few 
instances, such as those of gold, silver, and platinum, is 
effected by heat alone. The oxygen of the atmosphere 
unites with the sulphur, which is evolved as sulphur dioxide. 
In many cases, however, a portion of the oxygen combines 
with the metal, and an oxide instead of the free metal is 
obtained. The reduction of many of this class of ores con- 
sists simply in such interchanges. The application of heat 
and air in some instances converts the sulphide into a sulphate 
which in turn may be decomposed at high temperatures and 
separated into sulphur dioxide and a metallic oxide. On the 
other hand, some of the sulphides may, when heated with 
access of air, be converted into permanent sulphates capable 
of resisting high degrees of heat. The sulphides of the noble 
metals, when heated, part directly with the whole of their 
sulphur, leaving the metal in a pure state. Silver sulphide 
thus reduced is also partially oxidized, so that a small 
portion of argentic sulphate is formed, which requires for 
its reduction a still greater elevation of temperature. 

Agents, such as metallic iron, hydrogen, chlorine, etc., are 
frequently employed to combine with sulphur. If sulphide 
of lead be heated with iron, sulphide of iron and metallic 
lead result. This method is practised in the assay of galena, 
clean iron nails being heated with the ore. The sulphides 
of antimony, bismuth, copper, tin and silver are readily 
reduced by passing dry hydrogen over them at red heat, 
the result of the reaction being the free metal and hydrogen 
sulphide. Dry chlorine will also decompose them and com- 
bine with both the metal and the sulphur. Nitrohydrochloric 
acid converts the sulphides into chlorides, and hydrochloric 
acid in a few instances acts similarly; its hydrogen, com- 
bining with sulphur, is evolved as hydrogen sulphide. Strong 
nitric acid decomposes them, and is often employed in an- 
alyses of ores. The sulphur being thus oxidized, the liberated 



REDUCTION OF METALLIC COMPOUNDS 113 

metal combines with the acid to form a nitrate, mercuric 
sulphide or native cinnabar being the only ore which cannot 
be thus reduced. 

Oxides. — The reduction of lead, zinc, or tin, the working 
qualities of which have been impaired by frequent meltings 
with exposure to air, may be affected in the laboratory by 
placing the metal to be treated either in a large clay crucible 
or in the ordinary iron melting pot employed by dentists. 
The semioxidized metal is then covered with powdered 
charcoal, when the reaction described above takes place, and 
the original properties of the metal are restored. There are 
some oxides to which the foregoing treatment is not applic- 
able, but these may be reduced by passing a current of dry 
hydrogen over them when heated to redness. Makins gives 
the following very clear description of this method of reducing 
oxides : 

"A large two-necked bottle is fitted up in the usual way 
for the evolution of hydrogen. This has its delivery tube 
passed into a tube filled with fragments of calcium chloride, 
for the purpose of absorbing the moisture which may be 
carried over with the gas; to the other end of this drying 
tube is connected the tube which is to hold the metallic 
oxide (generally in a bulb blown upon this). The gas bottle 
should contain about a couple of quarts, so as to afford a 
steady supply; the calcic chloride tube should be long and 
well filled. In operating, after the gas has completely driven 
out the air in the apparatus, heat is applied to the bulb 
containing the oxide, and its reduction will be brought about. 
The gas must be kept up in a good stream, so as to drive out 
the watery vapor formed by the decomposition. Here the 
hydrogen takes the oxygen of the oxide, and water is formed, 
while the metal is set free." 

There are metals whose affinity for oxygen is so strong 
that their union with that element cannot be broken by such 
means as we have described. Deoxidation of these metals 
must be performed through the agency of some other metal 
possessing greater affinity for oxygen. For example, if 
oxide of iron be heated with potassium the iron will be 
8 



114 COMBINATION OF METALS 

deoxidized, while the potassium will be converted into (K2O) 
potassium oxide. 

Some metallic oxides may be reduced by heating with 
sulphur, part of the latter abstracting the oxygen, with which 
it unites to form sulphurous acid. A portion of the sulphur, 
however, unites with the metal, which is converted into a 
sulphide, or a sulphate, or a mixture of both. These must 
then be treated according to the directions already given for 
the reduction of metals when combined with sulphur. 

There are 4 also a few metallic oxides which chlorine gas 
will reduce. Thus, platinum is liberated from combination 
with oxygen when exposed to a current of dry chlorine. 

Probably the most powerful means of reducing metals 
from combination with non-metallic elements is that known 
as electrolysis. It consists in exposing a solution of a metallic 
salt to the decomposing influence of the galvanic current. 
A demonstration of this force may be made by taking a 
solution of lead nitrate and immersing in it a piece of zinc. 
The latter soon becomes covered with needle-4ike crystals 
of pure lead; the zinc replaces the lead, which is set free and 
decomposed at the point of galvanic action. Or, the same 
phenomenon may be witnessed by immersing a piece of clean 
iron in a solution of copper or a piece of copper in a solution 
of a salt of mercury, 1 the action only ceasing when all the 
metal in the solution is reduced. 

1 Reinsch's test for the detection of the mineral poisons is based on this 
principle. 



CHAPTER VII. 
LEAD. 

Symbol, Pb (plumbum). Atomic weight, 206.9. 

Occurrence. — In the free state it occurs in small quantities 
associated sometimes with a little antimony or silver. In 
combination as galenite or galena, PbS, usually with some 
silver, and frequently sulphides of antimony, bismuth and 
cadmium. Cerussite, PbC0 3 , the native carbonate is also 
a very important ore of lead. Among the less important 
ores of lead may be mentioned anglesite, PbSCX; pyro- 
morphite, Pb 5 Cl(P0 4 )8; wulfenite, PbMo0 4 . 

Historical. — Lead has been known from very remote times, 
although the material termed lead as used today differs from 
that mentioned in the very early writings of the Bible. The 
ores of lead are so comparatively easy to reduce, one may see 
how the ancients with their crude methods could very easily 
reduce this material. The metallurgical importance of lead 
may very easily be conceived when we stop to consider that 
the world uses nearly 900,000 tons of lead per year; this 
country produces nearly one-third of this amount. About 
one-half of the output from the United States was desilver- 
ized. Among the principal uses of lead may be enumerated 
the following: (a) Manufacture of white lead; (b) preparation 
of oxides of lead; (c) shot, lead pipe and sheet lead; (d) 
preparation of alloys. 

Reduction. — Three methods of smelting are available: 

1. Air-reduction Process. — The galena is first roasted to 
such a degree that a mixture of lead sulphide, oxide and 
sulphate is produced, and then the temperature is raised and 
the oxide and sulphate react with the remaining sulphide 
producing metallic lead and sulphur dioxide. 



116 LEAD 

Reactions : 

2PbO + PbS = 3Pb + S0 2 
PbS + PbS0 4 = 2Pb + 2S0 2 

2. Roasting and Carbon-reduction Process. — Roasting the 
galena until it is entirely decomposed or is practically con- 
verted into lead oxide mixed with a small amount of sulphate ; 
this is then reduced with carbon. Special procedures are 
used to recover the lead from the sulphate. 

Reaction : 

PbS + 2O2 = PbS0 4 

2PbS + 30 2 = 2PbO + 2S0 2 

PbO + C = Pb + CO, depending upon conditions 

2PbO + C = 2Pb + CO2 

3. Precipitation or Iron-redaction Process. — Galena is 
decomposed by heating with metallic iron, lead being set 
free and sulphide of iron and lead (lead matte) is produced. 

PbS + Fe = Pb + FeS. 

The process used is dependent upon conditions. The iron 
reduction process seems to be the simplest procedure, but 
this reaction is only carried on at a high temperature which 
would demand the presence of cheap fuel in the locality in 
which the reduction was carried on, also the presence of lead 
in the matte must be recovered by a subsequent treatment; 
both of these factors must be taken into consideration. 
From an economical point of view it has been found that the 
best practice is to make use of two or all of the above 
processes in the commercial reduction. 

The lead first obtained by any of these processes usually 
contains copper, antimony, tin, and other metals. These 
are removed by heating the metal in a shallow, flat-bottomed 
reverberatory furnace. Most of these metals oxidize before 
the lead, and collect in the dross which forms on the surface. 
This process is known as the softening of lead. The silver, 
which is always present is not removed by this process, but is 
extracted by one of the special methods for desilverizing 
lead described under Silver. 



PROPERTIES 117 

The wet processes are not used for the reduction of lead, 
but the electrolytic method has been tried in several localities. 
The lead is obtained from this process as a spongy mass. 
For the most part this method has not proved a financial 
success. 

Properties.— Lead is a bluish-white metal, with a distinct 
metallic luster when freshly cut; it loses its luster upon 
exposure to air due to the formation of the suboxide. Lead 
is sufficiently soft to be scratched with the finger-nail, 
ranking about 2 in the scale of hardness; it leaves a black 
streak when drawn across paper, and is generally considered 
the softest of the ordinary metals; the presence of other 
metals makes lead sensibly harder. It is a very poor con- 
ductor . of heat and electricity. Lead ranks low in tenacity, 
for this reason it cannot be drawn into a very fine wire 
although it may be rolled into sheets, and this form of lead 
was used at one time as a filling material in dentistry. When 
lead is fused and the temperature raised its surface assumes 
first a yellow and then a cherry hue and appears crystalline 
upon cooling; when partially solidified octohedral crystals 
belonging to the regular system are obtained. It melts at 
326° C, 618° F., boils white heat, vaporization begins at 
360°. Its specific gravity is 11.38. Specific heat 0.0314. 
Coefficient of linear expansion between 0° and 100° C, 
0.000028575. Coefficient of thermal conductivity in C. G. S. 
units is 0.081. As a conductor of electricity, 20.38. 

It has no taste but possesses a peculiar odor when freshly 
cut. Lead alloys with most metals with the possible exception 
of zinc, in the latter case it seems as if these two metals are 
without affinity and are only very slightly soluble in each 
other. Lead is a very important metal in the cupellation 
process in the separation of gold and silver from their ores. 

Lead possesses the property of solid flow to a remarkable 
extent ; advantage is taken of this fact in the manufacture of 
lead pipe, and it may be also pressed into wire of a much 
smaller gauge than could be obtained by the use of the 
draw-plate. 

In the manufacture of shot a small percentage of arsenic is 



118 LEAD 

added to the lead, this increases its hardness and also makes 
the lead flow more readily and assume the spherical form. 

From lead solutions, Zn, Mg, Al, Co and Cd, precipitate 
metallic lead. 

Solubilities. — Lead dissolves very readily in nitric acid, 
but sulphuric and hydrochloric acids are almost without 
action upon it in the cold. Hot concentrated hydrochloric 
acid slowly converts it into lead chloride. Sulphuric acid of a 
specific gravity higher than 1.6 attacks lead and the lead 
sulphate formed is soluble in the concentrated acid; this 
accounts for the presence of lead sulphate as an impurity 
in commercial sulphuric acid. 

Lead is soluble in pure water in the presence of air, forming 
the hydroxide; this compound is slightly soluble in water 
and may be a source of lead poisoning. As most of the potable 
waters contain carbon dioxide in solution, the lead hydroxide 
is precipitated from the water as the basic carbonate. 

Oxides. — Lead forms four oxides, Pb 2 0, PbO, Pb 3 04, Pb0 2 ; 
a fifth oxide is sometimes mentioned, Pb 2 03. 

Lead Suboxide (Plumbous Oxide), Pb 2 0. — Lead suboxide 
is a black oxide formed when lead is heated to its melting 
point. It may also be obtained by heating lead oxalate, 
PbC 2 4 , to 300° in a glass tube excluding air 

2PbC 2 4 - CO + 2C0 2 + Pb 2 0. 

When the suboxide is heated in air it burns, forming 
plumbic oxide. 

Pb 2 + O = 2PbO. 

Plumbic Oxide (Lead Monoxide, Litharge, Massicot), PbO. 
—Plumbic oxide is formed when lead is strongly heated 
in air and may be obtained by heating the nitrate or the 
carbonate. It is a yellowish powder and when heated melts 
and may be obtained in crystal form. Lead monoxide is 
soluble in acids and also in warm sodium or potassium 
hydroxide. With acetic acid in the presence of an excess of 
oxide it forms basic lead acetate which is used in medicine 
under the name "Goulard's Extract." 



DENTAL USES 119 

Lead Sesquioxide, Pb 2 3 . — Lead sesquioxide is described 
as an orange-colored precipitate formed when sodium hypo- 
chlorite is added to a solution of plumbic oxide in potassium 
hydroxide. This compound is generally considered a mixture 
of PbO and Pb0 2 . 

Triplumbic Tetroxide (Red Lead, Minium), PD3O4. — Tri- 
plumbic tetroxide, obtained by heating PbO for some time 
at a temperature slightly above 450°. At a higher tempera- 
ture it gives up its oxygen and is again converted into PbO. 

Plumbic Peroxide (Lead Dioxide), Pb02. — Plumbic per- 
oxide is obtained by fusing PbO with potassium nitrate or 
potassium chlorate. It is a brown-colored powder and a very 
powerful oxidizing agent. 

Dental Uses. — Lead is used in the construction of counter- 
dies. The prosthesis in constructing metallic bases generally 
obtains a counter-die of this metal by pouring the molten 
lead upon the die, which is constructed of some higher fusing 
metal or alloy. In crown and bridge-work a counter-die 
may be made in a similar manner or by simply hammering 
the die into a piece of lead. Lead being a very soft metal 
will not destroy the fine lines of the die in the latter process. 
Lead points have been used as a root canal filling material. 
It is also a constituent of the various low fusing alloys (see 
bismuth) . In riling lead or alloys containing large proportions 
of this metal coarse files should be used, as it is prone to cling 
to the rasps of the file and is very difficult to remove, thus 
ruining the file. In the form of shot, lead is also used in the 
process of swaging metals to a die, the shot being placed in 
some form of a retainer. This method is used when the die 
is constructed of a metal or alloy of a low fusing point, in 
which there is a liability of the molten lead injuring the die. 

Lead and mercury readily amalgamate ; this may be accom- 
plished by treating lead filings with mercury or by fusing 
the lead and mercury, then adding mercury. Lead amalgam 
is crystalline in structure and very brittle. 

As prepared by the first process the amalgam sets very 
slowly. I have specimens of this amalgam which were 
prepared seven years ago, and have been kept in tightly 



120 LEAD 

corked bottle. The mass is almost devoid of cohesive prop- 
erties, shows evidence of decomposition and when placed 
between the fingers emits a cringing sound showing it to be 
crystalline in nature. When prepared by the second method 
the amalgam has a metallic luster, may be readily carved 
with a penknife and a specimen one-half inch in thickness 
may be readily broken between the fingers. Upon standing 
it loses its metallic luster and resembles lead in color. This 
amalgam has no properties which would recommend it to be 
used in dentistry. Lead and gold are miscible in all pro- 
portions and form two compounds, AuPb 2 melting at 300° C. 
There is also a eutectic which melts at 215° C, corresponding 
to the formula AuPb 2 . These alloys are all very brittle and 
because of their comparatively low fusing point great care 
should be taken not to contaminate gold with lead. In 
swaging gold on a lead counter-die the surface of the gold 
should be protected from coming in actual contact with the 
lead, as there is a possibility of contamination. If the gold is 
placed in hydrochloric acid as a pickling solution the lead 
would not be removed, as lead is insoluble in this acid. Gold 
containing extremely small quantities of lead cannot be used 
for coinage. 

Silver and lead mix in all proportions. It forms a eutectic 
consisting of 98 per cent. Pb and 2 per cent. Ag., melting 
at 305° C It does not form chemical compound or mixed 
crystals. By taking advantage of this eutectic, silver may be 
recovered from lead as is described under Desilverization of 
Lead. 

Lead and platinum are said to form a peculiar alloy which 
has a low fusing point and very brittle. These two metals 
cannot be separated by cupellation, as the lead oxidizes; 
an alloy rich in platinum is formed which has a fusing point 
higher than the temperature of the muffle. 

Palladium forms a brittle alloy with lead. Tin and lead 
unite in any proportions, and these alloys are used as soft 
solders. Dr. Haskell's counter-die metal consists of 1 part 
tin and 5 parts lead. 

Antimony is alloyed with lead to increase its hardness. 



RESUME 



121 



Symbol, Pb. 
Valency, II and IV. 
Atomic weight, 206.9. 
Melting point, 326.9° C. 
Specific heat, 0.0314. 
Boiling point, 327° C. 
Malleability, 7th. 
Ductility, 8th. 



Resume. 

Specific gravity, 11.38. 
Crystalline form, octohedral. 
Chief ore, galena. 
Conductivity of electricity, 20.38. 
Conductivity of heat, 85. 
Coefficient of expansion, 

0.000029. 
Tenacity, 8th. 



CHAPTER VIII. 
MERCURY. 

Symbol, Hg (hydrargyrum). Atomic weight, 200.6. 

Occurrence. — Mercury occurs in nature in the native state 
sometimes containing a little tin, gold or silver. The sulphide, 
cinnabar HgS, is the principal ore. The ore is usually low 
grade and that found in this country yields on an average, 
less than 1 per cent, mercury. There is also a chloride, 
Hg 2 Cl 2 , horn mercury, but this is found only in small quan- 
tities. The chief mines are those of Almaden in Spain, 
Idria in Austria, California and the Bavarian Palatinate. 

Historical. — Mercury has been known from remote times 
and was considered as the type of the metallic character. 
One of the first endeavors of the alchemist, in his efforts 
to change base metals into gold or silver, was the fixing of 
the mercury, thus making the base metal non- volatile. In 
the fifteenth century the powerful medicinal properties of 
mercury were discovered; this fact together with the views 
held by the alchemists caused the study of mercury to be 
advanced at a very early period. 

Reduction. — There are three processes of reducing mercury 
from the sulphide ore; the first process is the one most 
commonly used at the present time. 

1. The sulphide ore is washed, whereby the sulphur is 
oxidized to sulphur dioxide and the metal liberated from 
combination. 

HgS + 2 = Hg + S0 2 . 

2. The sulphide is heated, in a closed retort with lime; 
calcium sulphide and sulphate are formed and the mercury 
set free. Reaction: 

4HgS + 4CaO = 4Hg + 3CaS + CaS0 4 

3. Cinnabar is heated with iron and the following reaction 
takes place: 

2HgS + Fc + 2 = 2Hg + FeS 4- SO>. 



PROPERTIES 



123 



In the first process the sulphide is heated in kilns where 
the reduction takes place. The temperature of the kilns is 
sufficiently high to volatilize the reduced mercury, the vapor 
of which passes into brick condensing chambers (Fig. 43, C) . 
For dental purposes the mercury is again distilled to remove 
the least trace of base metal with which it may be contami- 
nated. This product is known as redistilled mercury. 

Commercial mercury may also be purified by the electro- 
lytic process. By this method it may be freed from admix- 
tures of zinc, cadmium, bismuth, lead and tin. A crude 
test which is often used to discover if mercury contains base 
metal impurities is to allow some of the mercury to flow over 
a piece of white cardboard. If the mercury leaves a track or 




Fig. 43 

tail, base metals are present; however, mercury which will 
not show this reaction may still contain impurities in sufficient 
amounts to render it useless for dental purposes. 

Properties. — Solid mercury exists only at a temperature 
below —39.44° C, and at ordinary temperatures it is a liquid, 
being an exception to the general statement that metals 
are solids at ordinary temperatures. The solid metal is very 
ductile and is so soft that it may be cut with a knife. It 
ranks low in heat and electrical conducting powers, and also 
has a low coefficient of expansion on heating. During solidi- 
fication it contracts considerably, its specific gravity rising 
from 13.59 to 14.19 and forms octahedral crystals. Mercury in 
extremely thin films appears a violet color by transmitted light. 

Under a pressure of 760 mm. mercury boils at 357.25°, 



124 MERCURY 

giving a colorless vapor. Mercury does not tarnish upon 
exposure to the air and is classed as a noble metal. Mercury 
is obtained in the form of a dull gray powder when it is shaken 
up with oil or triturated with sugar, chalk, or lard. This 
operation is known as deadening, and is made use of in the 
preparation of mercurial ointments. The gray powder 
consists simply of very finely divided mercury in the form of 
minute globules. Most of the soluble salts and also the 
vapor of mercury is poisonous, and when an alloy containing 
mercury is heated to a temperature at which the mercury is 
volatilized care should be taken not to inhale the fumes; it 
is best to place the materials in a hood while heating. 

Solubilities. — Mercury is not attacked by alkalies. The 
most efficient solvent is nitric acid. It dissolves readily 
in the dilute acid hot or cold; with the strong acid, heat is 
generated, and with considerable quantities of material the 
action acquires explosive violence. Concentrated sulphuric 
acid at ordinary temperatures does not attack mercury, but 
with the hot acid sulphur dioxide and mercuric sulphate are 
formed. Hydrochloric acid even in the concentrated form 
has very little action on mercury; chlorine, bromine, and 
iodine, dry or moist attack the metal. Hydrobromic and 
hydroiodic acids attack mercury-forming mercurous bro- 
mides and iodide with the evolution of hydrogen. 

Compounds. — Mercury forms two oxides: Mercuric oxide, 
HgO, is a brick-red crystalline powder when prepared by 
prolonged heating of the metal, heating the nitrate or by 
heating a mixture of mercuric nitrate and mercury. Mercur- 
ous oxide is an unstable brown or black powder and may be 
prepared by adding sodium hydroxide to mercuric chloride 
solution. This compound when gently heated changes to 
mercuric oxide. Mercury forms two chlorides: Mercurous 
chloride, Hg 2 Cl2, known as calomel, is insoluble; mercuric, 
HgCh corrosive sublimate which is soluble. Mercuric 
chloride is a very valuable salt because of its antiseptic 
properties and is extensively used in medicine. 

Vermilion.- — With sulphur, however, mercury combines 
to form sulphates and sulphides. Of the latter we have 
mercuric sulphide (HgS), a compound of great interest to 



VERMILION 125 

dentists in consequence of its extensive use as a coloring 
pigment in vulcanizable rubbers and celluloid. It is the most 
common ore of mercury, and, as such, is termed cinnabar; 
when produced artificially it is known as vermilion. The 
best quality of the latter is made by the Chinese. Their 
process of manufacturing, for a long time a secret, consists 
in stirring a mixture of one part sulphur and seven parts of 
mercury in an iron pot; chemical union takes place, the 
result of the combination being a black powder. This is 
divided into small lots, which are emptied separately into 
suitable subliming pots, heated to redness. When a sufficient 
quantity has been placed in the pots they are covered up, 
and the heat is continued for thirty-six hours, with occasional 
stirring by means of an iron rod passed through the lid. 
Lastly, the pots are broken and the vermilion adhering to the 
upper portions levigated and dried. It may also be formed 
by rubbing 300 parts of mercury with 114 parts of flowers 
of sulphur, moistened with a solution of caustic potash. 
The resulting product, which is black, is then digested at 
about 49° C, with 75 parts of caustic potash and 400 parts 
of water, until it acquires a fine red color. 

Vermilion may be adulterated with red lead, sulphide of 
arsenic (As 2 S 3 ), ferric oxide, brick dust, or any cheaper sub- 
stance of a similar color; and the discomfort sometimes 
caused by wearing vulcanized rubber artificial dentures may 
be in part due to the presence of such deleterious substances 
as the arsenic and lead salts referred to. 

Tests for Vermilion. — In order to see at once whether a 
given red paint is cinnabar, minium (Pb 3 4 ) or ferric oxide, 
moisten the object with ammoniacal solution of AgN0 3 . It 
will turn black at once if it is HgS, due to the formation of 
Ag 2 S and HgN0 3 .3NH 3 . In order to see if a. given sample 
is all HgS or a mixture, heat some of it in a porcelain cru- 
cible to a red heat. If it evaporates, the paint is pure HgS. 

Vermilion is an inert mercurial compound, and both the 
black and the red varieties are quite insoluble in acids; 
only concentrated HX0 3 and aqua regia decompose it. It 
is unaffected by water, alcohol, or the alkalies. It is soluble 
in concentrated solution of K 2 S, Na 2 S,(NH 4 )2S, when these 



126 MERCURY 

sulphides contain KOH, NaOH or XH 4 OH. From the solu- 
tions colorless crystals of HgS, 2K 2 S, Hg.2Xa 2 S deposit, 
but water decomposes these double sulphides at once. It is 
also soluble in cold concentrated hydriodic acid and in warm 
dilute hydriodic acid. 

Pure vermilion, in combination with rubber, is not likely 
to produce deleterious effects when worn in the mouth, nor 
is it probable that this compound can be decomposed 
chemically and converted into a poisonous salt of mercury 
by mere contact with the saliva. The mechanical dentist 
will, however, do well to avoid the use of nitrohydrochloric 
acid in removing tinfoil from the surface. 

Regarding the presence of free mercury in rubbers before 
or after vulcanizing, Prof. Austen stated that the researches 
of Prof. Johnston with the microscope, and of Prof. Mayr 
by chemical analysis, failed to discover the slightest trace in 
samples of that which had been used by him for several 
years. Prof. Wildman observed that sulphur sublimed 
during vulcanization, but did not find the smallest trace of 
free mercury. Prof. Austen failed by mechanical force to 
press out any metallic globules, and during his entire experi- 
ence with indurated rubber as a base for artificial dentures 
never, even with the microscope, detected the slightest particle 
of metallic mercury upon the surface of any finished piece. 

If it is true, as some assert, that free mercury has occasion- 
ally been observed in rubber, then its presence must have been 
due to the use of an imperfect quality of vermilion ; but that 
the latter, when pure, is ever reduced during the process of 
vulcanizing, or by wearing in the mouth, is not at all probable. 

Amalgams or Mercury Alloys. — Mercury is miscible with 
most metals, in some cases chemical compounds are found 
and in others mixed crystals. (The amalgams will receive 
due consideration in Chapter XXIV.) 

Tin Amalgam. — Ordinary mirrors are made by covering 
one side of a polished glass plate with sheets of tinfoil, 
Upon the latter, mercury is rubbed by means of a soft brush; 
thus a crystalline film of tin amalgam forms on the glass. 

The alkali metals combine with mercury with a great rise of 
temperature. In contact with water these amalgams decom- 



AMALGAMS OR MERCURY ALLOYS 127 

pose; hydrogen being evolved, and the alkaline hydroxide 
formed. On this account sodium amalgam is frequently used 
in the laboratory as a reducing agent. Upon heating to 440° 
these amalgams leave behind crystalline compounds, K 2 Hg 
and Na 3 Hg, which spontaneously inflame in contact with air. 

The alkali amalgams are also used in the amalgamation 
process in the extraction of silver and gold from their ores. 

Zinc amalgams are only very slowly acted upon by dilute 
sulphuric acid; therefore by the superficial amalgamation 
of the zinc plates used for galvanic batteries, the same result 
is obtained as though the zinc were perfectly pure, and no 
solution of zinc takes place until the electric circuit is closed. 

Ammonium Amalgam. — When an amalgam of sodium and 
mercury is thrown into a solution of ammonium chloride, 
ammonium amalgam is formed. This amalgam may also 
be formed by passing an electric current through a solution of 
ammonium chloride or other ammonium salt, the solution 
standing over mercury which forms the cathode, the mercury 
begins to swell up to form five to ten times its original 
volume in absorbing 0.1 per cent, of its weight of ammonium. 
The sponge-like amalgam formed in the first process is 
generally believed to consist simply of mercury inflated by 
hydrogen and ammonia gas. When the mass is subjected to 
pressure it obeys Boyle's law, that is, its volume is in inverse 
proportion to the pressure. Upon standing this amalgam 
breaks up, liberating mercury, hydrogen, and ammonia; 
however, one-half of the hydrogen is occluded with the 
mercury. 

Resume. 

Symbol, Hg. Crystalline form (solid), iso- 

Valency, I or II. metric. 

Atomic weight, 200.6. Chief ore, sulphide, cinnabar. 

Melting point, -39.44° C. Conductivity of electricity, 

Specific heat, 0.0332. 1.69. 

Color, white. Conductivity of heat, 13. 

Boiling point, 357° C. Coefficient of expansion, 

Specific gravity, 13.59. 0.000181. 



CHAPTER IX. 
SILVER. 

Symbol, Ag (argentum). Atomic weight, 107.88. 

Occurrence. — Native silver is found in nature but not to 
the extent to which native gold occurs. Native silver may 
contain the following metals as impurities: gold, copper, 
platinum, mercury, bismuth and antimony. The native 
amalgam, Ag2Hg 3 to Ag 3 6Hg is found crystallized as iso- 
metric crystals. 

In combination silver occurs as: the sulphide, argentite, 
cerargyrite, horn silver, AgCl; also as the sulpho-arsenite 
and sulpho-antimonite. It is also found as impurities in other 
ores, as: manganese, lead and copper. Ordinary silver ore 
contains less than 1 per cent, of the silver compounds dis- 
tributed through various earthy minerals and shows the true 
nature of the silver-bearing substance in occasional rich 
specimens. Silver and its ores are found in the following 
localities: Norway, Teru, Northern Mexico, Michigan, 
Colorado, Montana, Idaho and Arizona, in the native 
condition; in combination, various parts of the United 
States, South America and Europe. 

Historical. — Silver 'is one of the longest known metals, 
possibly because of the fact that it occurs in the native 
metallic condition. 

Reduction. — The method of extracting silver may be 
classified into three groups: 

1. Dry processes. 

2. Wet processes. 

3. Electrolytic processes. 

To a certain extent the wet and dry methods of extraction 
are combined, argentiferous products obtained by dry methods 



AMALGAMATION PROCESS 129 

being worked up by wet methods, or vice versa. Electrolytic 
processes are usually preceded by a preparation of the ore 
by dry methods. 

The extraction of silver from ores and smelting products 
in the dry is based upon the conversion of the silver into a 
silver-lead alloy, while the combined wet and dry methods 
include : 

I. The conversion of silver into silver-lead alloy. 
II. The production of silver amalgam. 

III. The production of silver compound which is soluble 
in aqueous solution. 

Amalgamation Process. — The silver is first converted into 
the chloride by roasting with salt, the silver chloride 
formed is then reduced by metallic iron or copper and the 
reduced silver amalgamated. 

The chloridizing roasting of the ore is carried out in 
reverbatory furnaces and the reduction of the chloride 
and amalgamation of silver is effected in some form of 
amalgamating apparatus. 

The ore is first dried and then submitted to dry stamping; 
in some localities the sodium chloride for the next step in the 
reduction is also dried, the object of this procedure is to 
prevent the formation of sulphuric acid during the chlorid- 
izing. 

In the next step in the chloridizing roasting of the ores it is 
necessary that manganese dioxide be present in small 
quantities; if this is not present a certain amount of pyrites 
is added to decompose the salt. The chloridizing roasting is 
also an oxidizing roasting, the sulphides present being con- 
verted into oxides and sulphates. The free chlorine converts 
compounds of metallic sulphides with arsenic and antimony 
sulphides into metallic chlorides with the production of 
chlorides of sulphur, arsenic and antimony. The products 
of the roasting operation contains the greater part of the 
silver as chloride, together with some unaltered silver ore, 
also other metallic impurities. At the present time it is not 
customary to continue the roasting until all of the silver has 
been converted into the chloride, but the furnace is allowed 
9 



130 SILVER 

to cool slowly and a further chloridizing takes place. The 
result is that 95 per cent, of the silver may be converted 
into the chloride. 

Barrel Amalgamation. — The roasted ores still containing 
an excess of salt are first treated for some time with water 
and pieces of iron in rotating barrels. The salt dissolves in 
the water and the brine dissolves silver chloride, the iron 
reducing this to metallic silver. The barrels are agitated for 
a few hours and mercury is then added. The silver set free 
by the iron is then taken up by the mercury, forming an 
amalgam. The water is then drawn off and the amalgam is 
run off in troughs and collected. The amalgam is then 
pressed in canvas bags to separate the excess mercury. If 
the canvas bags are simply drained the mercury will contain 
only 0.06 per cent, of silver, while if the bags are pressed 
1.12 per cent, of silver is lost. The silver amalgam is then 
retorted in cast-iron tubes. 

The Patera Process. — This process is used in Central 
America and Mexico where fuel is scarce. The essential 
features of this process are: the ore is finely pulverized and 
the moistened ore is made into heaps after being intimately 
mixed with sodium chloride, copper sulphate and mercury. 
The mixture is then placed on floors impervious to mercury, 
generally made of asphalt or cement, it is allowed to partially 
dry, then mules or horses are driven over the mass and in 
this way trituration is obtained. The amalgam is collected 
by placing the ore in vats containing water. The collected 
amalgam is filtered through cloth bags and the mercury from 
the amalgam volatilized by heat. 

Dry Methods. — The extraction of silver from its ores in 
the dry way is effected by converting the metal into a silver- 
lead alloy and then submitting this to an oxidizing melting 
in the cupellation furnace. Lead possesses the property of 
readily alloying with silver and extracting the silver from 
various other compounds present in the ore; the operation 
is carried out either by simply melting or by a combination 
of roasting and melting processes. If the amount of silver 
in the lead is not sufficiently great to render direct cupellation 



AMALGAMATION PROCESS 131 

profitable, then it is concentrated before being cupelled. 
This concentration of the silver in the lead is effected by 
two processes, Pattinson's process and Parker's process. 

Pattinson's Process. — This process was described by 
Pattinson in 1833. He observed that if molten argentiferous 
lead be slowly cooled, the portions solidifying first are crystal- 
line and much poorer in silver than the still liquid portions. 
If the liquid portion be separated, it can again be separated 
into a poorer solid portion and still richer alloy, this separa- 
tion can be continued until the lead contains 2.5 per cent, 
silver. After this point is reached no further separation is 
possible and the liquid portion will have almost the same 
silver content. 

In the hand process, this process is carried out in hemi- 
spherical pots of cast-iron. They are usually 5 feet in 
diameter, 35 inches deep, 1\ inches thick at the bottom, 
and 1 inch thick at the top; each pot holds about 10 tons of 
lead. The lead is melted in the pot and any scum or dross 
forming on the surface is skimmed off and, if necessary, a 
further purification by poling is resorted to. When the lead 
is freed from impurities the fire in the grate is withdrawn 
or generally transferred to the grate of the adjoining pot, 
and the surface of the molten metal is carefully sprinkled 
with water. In consequence of the slow cooling which ensues, 
crusts form upon the surface and sides of the bath of metal, 
and these are thrust down and mixed up with the rest of the 
metal in order to insure a uniform reduction of tempera- 
ture. As soon as the surface of the bath becomes uneven 
and the metal is of an almost semipastry consistency, crys- 
tallization is sufficiently advanced and the work of ladling 
out the crystals begins. This is effected by two or more 
workmen, working at one or on two opposite sides of the 
pot with perforated ladles, and either § or J of the contents 
of the pot is removed as crystals, according to whether the 
thirds or eighths system of working is in use. The volume 
of the crystals ladled out is measured by means of a right- 
angled measure laid across the top of the pot. 

The enriched third or eight of the original lead is either 



132 SILVER 

ladled out of the pot into an adjoining one in the system of 
thirds or else cast into molds. The crystals obtained in 
this way are small elongated octohedra united along an edge, 
which, as they only grow in one direction appear as long, 
four-sided pyramids. 

To the crystals which have been ladled over, a quantity 
of lead of the same silver content is now added, so that the 
pot again contains its normal quantity; that is, with the 
thirds system J of the normal contents of the pot. To the 
mother liquor remaining behind, f of the volume of the pot 
of lead of the same silver content as the mother liquor must 
be added. Then in most cases the operation of the desilver- 
ization is repeated just as the case of the pot full of the original 
lead. In the thirds system, the entire quantity of argentif- 
erous lead is in the pots, of which there may be 15 in number. 

In the system of eighths, from 2 to 6 pots are worked to- 
gether but the process does not go on uninterruptedly as in 
the thirds system until lead of the requisite content is pro- 
duced. The following is a description of the thirds system 
(Freiburg) in which 14 pots are used. The lead contain- 
ing 0.02 per cent, of silver is changed in the pot No. 7 
and after it is melted and cooled, f of its contents in crystal 
form are ladled to pot 8, the remaining liquid J being 
put into pot No. 6; in order that fresh crystallization can be 
effected in pots 6 and 8, they have added to them § and ^ 
respectively of the contents of lead of the same percentage 
of silver as each of them contain, from stock reserves. The 
contents of both of these pots are now melted and allowed to 
crystallize, and then f of the contents of pot No. 6 crystals 
are ladled out into pot No. 7 and the remaining §• of the 
molten liquid is put into pot ,No. 5; from the eighth pot 
the crystals are ladled to pot No. 9 and the mother liquid 
go to pot No. 7. Pot No. 7 has in this way received another 
full charge, while pots Nos. 5 and 9 are made up of the 
requisite quantity by the addition § and J respectively. 

Pots 5, 7, and 9 are crystallized and after them 4, 6, 8, 
and 10; and by continuing the working in this way, poor lead 
is at last obtained with 0.002 per cent, of silver and rich 



AMALGAMATION PROCESS 



133 



lead with at least 1.5 per cent, of silver. The silver from the 
rich lead may be recovered either by cupellation or submitted 
to the zinc desilverizing process. 

Zinc Desilverizing Method (Parker's Process). — If 1.5 to 
2 per cent, by weight of zinc is added to argentiferous lead 
in the molten condition and thoroughly stirred, then allowed 
to cool, a crust or sciim forms upon the surface as the tem- 




Fig. 44 



perature is allowed to fall. This scum is a solidified mixture 
of alloys of lead, zinc and silver, lighter than the molten 
lead and containing all the silver originally present in the 
lead, and can be easily separated from the rest of the metal. 
The zinc and lead can then be driven off from the silver by 
distillation and cupellation. 

The cupel (Fig. 44) is made of a fire-clay mixture, in the 
hearth of a reverberatory furnace; r represents the muffle 



134 SILVER 

which has a concavity oval in shape. The rich lead is placed 
in the muffle and brought to redness, and air is blown over 
the surface. Lead changes to lead oxide, which runs off until 
finally only silver, with some 5 per cent, of lead, remains. 
This is refined in a new hearth and with higher heat. 

Wet Process (Zieroogel Process) . — When argentiferous 
pyrites, or an artificially formed regulus containing sulphides 
of silver, copper and iron is roasted, the sulphides are first 
converted into sulphates and, as the roasting continues, 
first the iron, tin, copper and lastly the silver sulphate is 
converted into oxide. By carefully watching the process 
all of the iron and part of the copper sulphates are decom- 
posed. On lixiviating the roasted mass with water, the silver 
sulphate together with the remainder of the copper sulphate 
dissolves. From this solution the silver is precipitated by 
scrap copper. 

The Percy-Patera Process. — The ore is roasted with salt 
and the silver chloride so formed is then extracted by means 
of sodium thiosulphate 

Na 2 S 2 3 + AgCl = NaCl + NaAgS 2 3 . 

To this solution so obtained sodium or calcium sulphide is 
added which precipitates silver sulphide 

2NaAgS 2 3 + Na 2 S = Ag 2 S + 2Na 2 S 2 3 . 

The silver sulphide is then reduced by roasting in a rever- 
beratory furnace. 

The electrolytic process requires the conversion of the 
silver into a copper-silver, lead-silver, zinc-silver or gold- 
silver alloy and the silver collects at the anode (positive pole) 
in all cases except when gold-silver alloy is used, and then it 
collects at the cathode (negative pole). The silver which is 
deposited contains various impurities which must be removed 
by special processes. Preparation of chemically pure silver. 

Pure Silver. — Pure silver, which is reckoned as 1000 fine, 
may be obtained from standard or other grades of silver by 
dissolving the granulated metal or copper alloy in HN0 3 , 
sp. gr. 1.20 (cone. HN0 3 with an equal volume of distilled 



PURE SILVER 135 

water). Heat facilitates the solution of silver in the HN0 3 . 
Dilute the solution with 20 volumes of distilled water. Add 
HO so long as precipitate keeps forming, stir vigorously and 
let settle. Drain off the liquid and wash with cold water 
until filtrate shows no trace of copper. Boil the silver chloride 
with aqua regia (1 to 3) for a greater or less time, according 
to quantity, one hour for 100 grams, two hours for 500 grams. 
Drain again and wash with distilled water, until all acidity 
has been removed. Now add 10 per cent, solution KOH 
so that the KOH in it equals the weight of silver chloride; 
add an equal amount of pure glucose and boil until chloride 
has become a dark gray, fine metallic powder; drain and 
wash thoroughly until all alkali reaction disappears. Dry 
the powder at about 150° C. It is pure silver, and is kept 
best in this shape for use in the laboratory. You may melt 
it, or some of it, in a cavity on a purified piece of charcoal, 
or in a crucible which has been lined with pure charcoal 
powder. In the first case use the Bunsen gas blow-pipe, 
in the second a gas or wind furnace. Pouring the molten 
metal from a height of several feet into water will convert 
it into granules. In hammering or rolling silver it must be 
heated to redness at regular intervals, as the mechanical 
shocks cause a certain brittleness, the metal tears at the 
edges. 

Another method of precipitating silver in the metallic 
form consists in placing a sheet of copper in a solution of 
argentic nitrate. The metal is thrown down in a crystalline 
form. Silver thus obtained is never free from traces of 
copper. 

Pure silver can be obtained by fusing the pure chloride 
with sodium carbonate. The reaction is shown in the 
equation : 

2AgCl + Na 2 C0 3 = 2NaCl + C + C0 2 . 

Owing to the copious evolution of carbon dioxide which 
takes place during the decomposition, some of the silver may 
be thrown from the crucible, and loss may occur by the 
absorption by the crucible of some of the fused chloride. To 



136 SILVER 

avoid this the sides of the vessel should be coated with a hot 
saturated solution of borax. 

A mixture of 100 parts of argentic chloride, 70.4 of calcium 
carbonate (chalk), and 4.2 of charcoal has been recommended 
as a means of obtaining pure silver. This mixture is heated 
to dull redness for thirty minutes, and then raised to full 
redness; carbon dioxide and carbon monoxide are given off; 
the calcium chloride is converted into calcium oxychloride, 
underneath which, in the bottom of the crucible, will be 
found the button of pure silver. 

Electrolytic processes are also used and the nature of the 
deposit of silver is dependent upon the acid radicle present 
in the solution. The pyrophosphate gives a crystalline 
deposit of silver, while the nitrate radicle produces a black 
powder. 

Properties. — Silver is a pure white metal having a perfect 
metallic luster. The color of silver is taken as the type for 
the color of white metals and these metals are spoken of as 
silvery white in color. It is harder than gold and softer than 
copper. The specific gravity of silver is about 10.42. Silver 
is the best conductor of heat and electricity and the con- 
ductivity of other metals is generally compared with that of 
silver. The melting point, as determined by Becquerel, is 
960° C, but the more recent determination Berthelot places 
the fusing at 962°. Upon solidification silver forms crystals 
belonging to the isometric system and the latent heat of 
fusion is 21.07 calories. At about 1955° C. silver volatilizes, 
yielding a green vapor and can be distilled by means of the 
oxy hydrogen blow-pipe. Thin films of silver appear blue 
by transmitted light. 

If ferric citrate be added to the silver nitrate, a red solution 
and lilac precipitate of free silver can be made. The latter 
after washing with ammonium nitrate gives a red solution 
in water. The silver is present in a very finely divided state 
and is known as "colloidal" silver. 

If mercury be added to a solution of silver nitrate a pre- 
cipitate of metallic silver will be formed in a short time, 
resembling real vegetation, this is called the "silver tree." 



PROPERTIES 137 

Nearly all of the metals precipitate metallic silver from a 
solution of its salts. 

Many different methods have been used to whiten the 
surface of silver objects, Gee's method of whitening consists 
in making the silver red hot, and then boiling in 2.5 per cent, 
solution of sulphuric acid. 

Silver articles are sometimes finished with what is called 
the oxidized finish. There are two distinct shades in use, one 
produced by a chloride, which has a brownish tinge, and the 
other by sulphur having a bluish-black tint. The following 
is said to produce a very fine bluish-black tint. The silver 
piece is washed with a solution containing copper sulphate, 
ammonium chloride and acetic acid. The article is then 
warmed and placed in a warm solution of either sodium or 
potassium sulphide. 

In the molten state silver absorbs twenty-two times its 
volume of oxygen and during solidification the gas is expelled, 
causing the formation of small blisters; this is spoken of 
as the spitting of silver. The spitting of silver may be 
entirely prevented by the admixture of small quantities of 
copper, bismuth, or zinc to the silver. 

Silver is not acted upon by atmospheric oxygen, but is 
quickly tarnished by traces of hydrogen sulphide in the air. 
The blackening of silver in air may be prevented by coating 
the silver with collodion diluted with alcohol. To remove the 
tarnish, potassium cyanide or sodium hyposulphite solutions 
may be used. It is claimed that silver utensils darkened from 
use may be brightened by boiling in a bright aluminum vessel 
with soapy water. 

In malleability silver ranks second to gold, and in ductility 
is exceeded by gold and according to later experimentation, 
platinum. There is no scientific foundation to the ranking 
of metals according to malleability and ductility, and the 
tables given upon these properties are for the purpose of 
simply giving the student some idea of malleability and 
ductility. As our methods of determining these properties 
are improved upon, there is no question but that these tables 
will be very greatly altered. 



138 SILVER 

Compounds. — Silver forms one oxide corresponding to the 
formula Ag 2 0, although two other oxides, Ag 2 2 and Ag 4 0, 
are believed to exist. 

Silver monoxide, Ag 2 0, is obtained by adding sodium or 
potassium hydroxide to a solution of silver nitrate. A brown 
precipitate consisting of hydrated oxide is found, which when 
heated is converted into the anhydrous compound. When the 
carbonate is heated to 200° this oxide is also found. 

Upon heating silver monoxide to 260° it begins to reduce 
with the liberation of oxygen and metallic silver. These 
reactions characterize silver as a noble metal. 

When silver oxide dissolves in ammonia a very explosive 
compound, fulminate of silver, is found, and is believed to 
have the formula AgN 3 . 

Silver chloride, AgCl, is a white, curdy precipitate pro- 
duced when a soluble chloride is added to silver nitrate. It 
melts at 451° to a yellowish liquid which congeals to a horny 
mass. When exposed to light this compound darkens, 
assuming a violet tint, and finally becoming dark brown. 
This compound is used in photography. 

Silver nitrate, AgN0 3 , is obtained by dissolving silver in 
nitric acid. It forms large, colorless, rhombic crystals which 
melt without decomposition at 218°. This is a very important 
compound and is used in dentistry because of its therapeutic 
effect. It is also used whenever a soluble silver salt is desired. 

Silver Cyanides, AgCN. — This compound is prepared by 
adding potassium cyanide to a solution of silver nitrate. 
Two conditions are met with, depending upon the quantity 
of cyanide used. 

I. AgN0 3 + KCN = AgCN + KN0 3 

This reaction takes place when only a small quantity of 
cyanide is added, and silver cyanide, being insoluble, pre- 
cipitates from the solutions. 

When an excess of potassium cyanide is added, the follow- 
ing is formed: 

AgCN + KCN = KAg(CN) 2 



ALLOYS 139 

This silver potassium cyanide is used in eletroplating. 
The double salt breaks down and the silver is deposited as a 
uniform metallic coating. 

Solubilities. — The fixed alkalies do not attract silver, hence 
silver crucibles are used instead of platinum for fusion with 
caustic alkalies. 

Ammonium hydroxide dissolves finely divided silver, in the 
presence of air. Nitric acid, both dilute, and concentrated, 
dissolve silver readily. Dilute sulphuric is without action 
upon it except when the silver is in the finely divided state. 
Hot concentrated sulphuric acid dissolves silver with the 
formation of silver sulphate, sulphur dioxide and water. 
Hydrochloric acid is without action upon it, but the metal is 
readily attacked by chlorine, bromine, or iodine. Silver is 
soluble in potassium cyanide in the presence of air: 

2Ag + 4KCN + H 2 + O = 2KAg(CN) 2 + 2KOH. 

From this solution the silver may be again precipitated 
by heating with metallic zinc, lead or hydrochloric acid. 
The " cyanide process" for the recovery of gold and silver is 
based upon this reaction. 

Alloys. — At ordinary temperatures mercury and silver 
unite very slowly but upon heating the two unite much more 
readily. Another method of preparation is by treating a 
solution of silver nitrate with mercury. This causes the 
silver to be precipitated in a finely divided state and then 
upon shaking the amalgam is formed. Several compounds 
are said to be formed. 

Copper and Silver. — The two metals are miscible in all 
proportions in the fluid state and it requires heating for 
some time before the mass becomes homogeneous. Fenchel 
states that an alloy containing 2 per cent, of silver with 
copper, shows free silver after being kept fluid for ten hours. 
Alloys containing 96 or 97 per cent, of silver are found to be 
homogeneous after eight to ten hours' heating. Copper is 
alloyed with silver to increase the hardness of the latter 
metal, this prevents the loss of silver by attrition. Coin 
silver contains from 900 to 925 parts of silver to the 1000, 



140 SILVER 

and from 75 to 100 parts of copper. Standard silver is 
silver so alloyed. 

The following is a list of the proportions of copper and 
silver in the silver (coin) of some of the nations: 

United States 

France 

England 

Indian rupees 

German-Prussian thalers .... 
Prussian silver'groschen .... 



silver 900, 


copper 100 


" 900, 


" 100 


" 925, 


75 


" 947, 


53 


" 811, 


" 187 


" 283, 


u 717 



Gold and silver readily alloy and Fenchel states that the 
fusing point of gold is hardly lowered even by the addition 
of silver up to 50 per cent. The tensile strength of gold is 
increased by alloying with silver. Gold-silver alloys are 
soluble in boiling sulphuric acid, the silver dissolving, leav- 
ing the gold unchanged; when the proportion of gold to silver 
is not greater than 4 to 7 in an alloy nitric acid dissolves the 
silver and the gold remains unchanged. 

Platinum and Silver. — Platinum and silver alloy and the 
fusing point depends upon the percentage of platinum 
present. An alloy of these two metals, say 10 per cent, 
platinum, may be prepared by melting the silver and then add- 
ing platinum in the form of a thin ribbon. The alloy thus 
prepared should be heated for some time to ensure perfect 
mixture of the two metals. Dental alloy, used to some extent 
in Europe for the construction of dental bases, contained from 
25 to 30 per cent, of platinum with silver. The object of 
alloying the platinum with silver is to increase the resistance 
of silver to the action of chemicals. These alloys containing 
10 per cent, of platinum are attacked by nitric acid and both 
platinum and silver are dissolved. Sulphur also attacks this 
alloy-forming sulphide of silver. At the present market 
price of platinum, there is no occasion for the use of this alloy. 

Lead and Silver. — Lead is miscible with silver in almost all 
proportions, and because of the ready alloying of these two 
metals lead is used to dissolve silver from its ores in the 
process of assaying. The old saying is " that all lead contains 
silver" is for the most part true, and in test — lead used in the 



SILVER SOLDERS 141 

above process (assaying) — allowance must always be made for 
the silver already present in the lead. Zinc alloys readily 
with silver and these two metals seem to have more of an 
affinity for each other than lead has for silver. The 
Parker's process of desilverizing lead proves this state- 
ment. Zinc will prevent lead from spitting and also interferes 
with the oxidation of other metals when alloyed with silver. 

Silver Solders. — Silver solders are used to solder German 
silver, brass, copper, silver and silver alloys. Silver solders 
are classed as hard solders because they require red heat to 
fuse. They consist of alloys of silver, copper and zinc. 

Richardson's Mechanical Dentistry gives the following 
formulas for these solders: 

No. 1. 

Silver 66 parts 

Copper . 30 " 

Zinc 10 " 

No 2. 

Silver 6 pennyweights 

Copper 2 

Brass 1 " 

No. 3. 

Silver 5| pennyweights 

Brass 40 grains 

Dr. Kirk recommends the following compositions: 

Fine silver. Copper. Brass. Zinc. 

4.0 .. 3.0 

2.0 .. 1.0 

19.0 1.0 10.0 5 

66.7 23.3 .. 10 

50.0 33.4 16.6 

11.0 .. 4.0 1 

Van Eckart's alloy, employed to some extent in France 
as a base for artificial dentures, is composed of the following 
proportions: silver, 3.53; platinum 2.40; and copper 11.71. 
It is very elastic (which property it does not lose by annealing) 
and can be highly polished. 



142 



SILVER 



Resume. 



Symbol, Ag. 
Valency, 1. 

Atomic weight, 107.88. 
Melting point, 964° C. 
Specific heat, 0.057. 
Malleability, 2d. 
Tenacity, 4th. 
Color, white. 
Boiling point, 1955° C. 



Specific gravity, 10.42 to 

10.52. 
Crystalline form, isometric. 
Chief ore, horn silver. 
Conductivity of electricity, 1st. 
Conductivity of heat, 1st. 
Coefficient of expansion, 

0.00001909. 
Ductility, 2d. 



CHAPTER X. 
BISMUTH. 

Symbol, Bi. Atomic weight, 208. 

Occurrence. — Bismuth occurs for the most part in the native 
state. The native metal is often alloyed with arsenic or 
impure with sulphur or tellurium. Native bismuth occurs 
in crystalline rocks, and clay slate associated with ores of 
cobalt, nickel, gold, lead and zinc, also with molybdenite, 
wolframite and scheelite. Bismuth is found intimately mixed 
with other minerals, as with tin ore in Bolivia; Cobalt in 
Saxony and gold-bearing iron ore in Queensland, Australia. 

The principal localities from which the native metal is 
obtained are the following: Saxony and Bohemia, Chili, 
Sweden, Norway and Australia. The native metal is not 
found in any quantities in the United States, however, some 
is obtained from South Carolina. 

Other ores of bismuth are : bismuthite or glance, sulphide, 
Bi 2 S3. Telluride, carbonate and bismuth oxide, B12O3. 

Bismuth is one of the comparatively rare, useful metals; 
and its commercial value is generally at least ten times the 
cost of antimony. 

Reduction. — Native Metal. — In refining the native metal 
the ore is broken up and liquated by being heated in inclined 
pipes, when the bismuth readily melts and drains off from the 
earthy impurities. As obtained from this process the bismuth 
contains impurities, and in order to obtain pure bismuth, 
wet methods must be used. 

The impure metal is dissolved in nitric acid forming 
Bi(N0 3 )3 and then precipitated by the addition of water. 

Bi(N0 3 ) 3 + 2H 2 - (BiO)N0 3 + 2HN0 3 . 



144 BISMUTH 

The basic nitrate is next dried and heated in a crucible 
with charcoal; the salt is first converted into the trioxide 
Bi 2 03 by the action of heat and then reduced by the carbon : 

2(BiO)N0 3 ,H 2 = Bi 2 3 + N2O4 + O + 2H 2 
Bi 2 3 + 3C = 3CO + 2Bi. 

The method made use of in Saxony, where most of the 
bismuth of the world is produced, the ores are first roasted 
to free them from sulphur, arsenic and other volatile con- 
stituents. After they are roasted they are smelted in crucibles 
with iron, charcoal and slag, the melted bismuth settling 
out in the bottom of the crucible; or the roasted ore may 
be treated with strong hydrochloric acid which dissolves 
the impure bismuth and from which it is precipitated as 
oxychloride by the addition of water. The metal may be 
further purified electrolytically. 

Properties. — Bismuth is a lustrous white metal, with a 
faint reddish tinge, it closely resembles antimony in appear- 
ance ; however, antimony is a white metal, and bismuth when 
compared with antimony shows a distinct reddish cast. It 
is hard and so brittle that it may readily be ground to a 
powder in a mortar. Bismuth may be said to be devoid of 
malleability and ductility. It is also a poor conductor of 
heat and electricity. Bismuth is unacted upon by dry air 
or oxygen. The melting point of bismuth is 270° C, and its 
specific gravity 9.82. It expands upon solidification and 
imparts low fusing properties to its alloys; however, it also 
makes the alloys more or less brittle. Small quantities of 
bismuth renders gold and silver brittle when alloyed with 
them and also reduces the conductivity of copper. Rhombo- 
hedral crystals of bismuth may be obtained when the metal is 
fused and allowed to cool slowly; these crystals form at the 
edges of the metal and may be obtained by decanting the 
still fused portion of the metal. Its position in the electro- 
motive series is between copper and silver and it therefore 
inclines toward the noble metals. 

Compounds. — Bismuth is said to form three oxides: 

Bi 2 3 , B12O4 and Bi>0 5 . 



LOW FUSING ALLOYS 145 

Bismuth dioxide is a pale yellow powder and when treated 
with sulphuric acid, bismuth and bismuth sulphate are 
formed. 

Bismuth trioxide is the most important oxide and when the 
two remaining oxides are heated in air the trioxide is formed. 
It is a light yellow powder, readily fusible, forming a vitreous 
mass on cooling. 

Bismuth tetroxide, Bi 2 4 , is possibly a mixture of Bi 2 03 and 
Bi 2 5 ; Bi 2 3 + Bi 2 5 = 2Bi 2 4 . 

Bismuth hydroxide, Bi(OH) 3 , is formed by precipitating 
a bismuth salt with the alkali hydroxides; upon drying 
Bi(OH) 3 forms the oxyhydroxide BiO(OH). 

Bismuth trichloride is prepared by passing dry chlorine 
gas over powdered bismuth, gently heated in a retort. When 
this salt is treated with water a precipitate of BiOCl, bismuth 
oxy chloride is formed. The formation of this compound is a 
means of identifying bismuth in solution. 

Bismuth nitrate is prepared by dissolving bismuth in 
nitric acid. 

The subnitrates represented by various formulas may be 
prepared from the nitrate by adding much water to the solu- 
tion of the salt. 

Solubilities. — The best solvent for bismuth is nitric acid; 
hydrochloric acid is without action upon it. Cone, sulphuric 
dissolves bismuth with the evolution of sulphur dioxide. 
When placed in chlorine it unites with it, with the evolution 
of light. 

Alloys. — Bismuth is said to form an adhesive mass with 
mercury, which contracts upon setting. 

Low Fusing Alloys. — These alloys are used as safety plugs 
in automatic sprinklers and also in dentistry to construct 
dies for crown and bridge-work. 

Wood's metal is composed of bismuth 4, lead 2, tin 1, and 
cadmium 1 part; fusing point, 60.5° C. 

Rose's metal: bismuth 2, lead 1, and tin 1 part; melting 
point, 93.75° C. 

Lichtenberg's metal: bismuth 5, lead 3, tin 2 parts; 
melting point, 91.6° C. 
10 



146 



BISMUTH 



Mellotes (Newton's) metal: bismuth 8, lead 5, tin 3 parts; 
melting point, 94.50° C. 



Resume. 



Symbol, Bi. 
Valency, III or V. 
Atomic weight, 208. 
Melting point, 270° C. 
Boiling point, 1420° C. 
Color, reddish tinge. 
Specific heat, 0.0308. 
Ductility and malleability, 
brittle. 



Specific gravity, 9.82. 

Crystal form, rhombo- 
hedral. 

Chief ore, native bismuth. 

Conductivity of heat, 18. 

Conductivity of electric- 
ity, 1.22. 

Coefficient of expansion, 
0.000013. 



CHAPTER XI. 
COPPER. 

Symbol, Cu (Cuprum). Atomic weight, 63.57. 

Occurrence. — Copper is found in the native state in various 
localities, notably in the Lake Superior region. In combina- 
tion copper is a very abundant element and is widely dis- 
tributed. The most important ores are the following : 

Ruby ore, Cu 2 0; copper glance, Cu 2 S; copper pyrites, 
Cu 2 SFe 2 S3; purple copper ore, Cu 3 FeS 3 ; malachite, CuCO 2 - 
Cu(OH) 2 ; azurite, 2CuC0 3 .Cu(OH) 2 . 

Historical. — Copper has been known to mankind from the 
earliest ages, and probably in the form of bronze was the 
first alloy made use of. 

Reduction. — The method of reduction depends upon the 
ore used; the carbonate and oxide may be reduced by 
smelting the ore in a blast furnace and then reducing with 
coke or coal, according to the reaction: 

Cu 2 + C = CO + 2Cu. 

In the case of mixed ores containing sulphides, the process 
consists of six distinct stages: 

1. The ores containing on an average 30 per cent, iron 
and 13 per cent, copper, are first calcined; usually in a 
reverberatory furnace (Fig. 45); the sulphur is burned to 
sulphur dioxide and the metals are partially oxidized. 

2. Fusing the calcined ore in a furnace (Fig. 46) when the 
copper oxides formed during the calcination react upon a 
portion of the ferrous sulphide, with the formation of cuprous 
sulphide and ferrous oxide: 

CuO + FeS = Cu 2 S + FeO 
2Cu 2 + 2FeS = Cu 2 S + 2FeO + S. 



148 



COPPER 



The oxide of iron combines with the silica present to form 
a fusible silicate of iron or slag which contains little or no 




Fig. 45 



copper. This is run off, leaving a regulus containing 30 to 
35 per cent, copper and known as course metal consisting of 




Fig. 46 



cuprous and ferrous sulphides. The course metal is granu- 
lated by allowing it to flow into water. 



REDUCTION 149 

3. The granulated course metal is again calcined, which 
results in the oxidation of more of the sulphur as the dioxide, 
and the dioxide and the partial oxidation of more of the 
metals. 

4. The calcined mass is then fused with some refinery slag, 
which results in the production of a regulus consisting of 
nearly pure cuprous sulphide, the greater part of the iron 
having passed into the slag. The regulus, called fine-metal 
or white-metal, contains 60 to 75 per cent, copper. 

5. This operation consists of roasting the white-metal in a 
reverberatory furnace. A portion of the cuprous sulphide 
is reduced to cuprous oxide, and as the temperature rises 
reacts upon another portion of cuprous sulphide. The reac- 
tions which occur in this step are as follows: 

2Cu 2 + Cu 2 S = 6Cu + S0 2 

3Cu 2 + FeS = 6Cu + FeO + SO2. 

The metallic copper thus obtained has a blistered appear- 
ance and is known as blister-copper. 

The impure copper is melted down upon the hearth of a 
reverberatory furnace in an oxidizing atmosphere. The 
impurities present such as iron, lead, and arsenic are first 
oxidized in a suitable furnace represented in Fig. 47, and the 
oxides are either volatilized or combine with the siliceous 
matter to form a slag. The oxidation is continued until the 
copper begins to oxidize; when the oxide thus formed reduces 
any cuprous sulphide present with the evolution of sulphur 
dioxide. Finally the oxide of copper present is reduced with 
coal and stirred with poles of wood. 

Wet Process. — Copper present in burned pyrites obtained 
from the manufacture of sulphuric acid, which may contain 
3 per cent, copper, are subjected to a smelting process. When 
this material is smelted with 12 to 15 per cent, of common salt, 
the copper is converted into cupric chloride. The mass is 
treated with water, the cupric chloride dissolves, and metallic 
copper can be precipitated by means of scrap-iron, or by 
electrolysis. 



150 



COPPER 



Electrolysis. — Copper may also be reduced by electrolysis, 
but the expense entailed is too great in most cases. When a 
high grade of purity is demanded, this process may be used 
and a grade of copper containing about 0.02 part in a thou- 
sand may be obtained. 




Fig. 47 



Properties. — Copper is a lustrous metal having a reddish- 
brown color. The native metal is found crystallized in regular 
octahedra, and small crystals of the same kind may be 
obtained by the slow deposition of the metal from solution 
by reducing agents. On account of its chemical resistibility, 
its good mechanical properties, and its melting point, copper 
is largely used for utensils of all kinds. Another great sphere 
for the application of copper depends upon its great conduc- 
tivity for the electric current. In this respect it is only 
exceeded by silver. For this purpose it must be in the pure 
condition, as small quantities of impurities lessen its con- 
ductivity. 



SOLUBILITIES 151 

Copper is an extremely tough metal and can be readily 
rolled into sheets or drawn into wire. It ranks fourth in 
malleability, fifth in ductility, and second in tenacity. As a 
conductor of heat and electricity it ranks second to silver. 
Its melting point is about 1050° C, and its boiling point, 
2310° C. Copper possesses the property of absorbing gases, 
among which may be mentioned carbon monoxide, sulphur 
dioxide and hydrogen- Oxygen is absorbed in the same 
manner as silver and forms bubbles upon the surface of the 
cast copper. The molten metal dissolves cuprous oxide while 
fusing and this tends to affect the physical properties of the 
metal. Copper is only slowly acted upon by exposure to dry 
air, but in the presence of atmospheric moisture and carbon 
dioxide, it becomes coated with a greenish basic carbonate. 
When volatilized in the electric arc, copper gives an emerald- 
green vapor. Copper leaf transmits greenish-blue light. 
Solutions of copper are reduced to the metallic state by 
Zn, Cd, Al, Pb, Fe, Co, Ni, Bi, Mg. A bright strip of iron 
in solution of cupric salts acidulated with hydrochloric acid, 
receives a bright copper coating, recognizable from solutions 
in 120,000 parts of water. 

Arsenic in small quantities has no injurious effects upon 
copper unless the percentage is 1 per cent, or over, then the 
copper becomes brittle when rolled at an elevated temper- 
ature. 

Antimony in small quantities does not affect the ductility 
of copper. Copper containing 0.529 per cent, of antimony 
can be drawn into the finest wire just as well as pure copper. 
However, both arsenic and antimony, present to a few 
thousandths of 1 per cent., affect the conductivity of 
electricity of copper. 

Solubilities. — Copper does not dissolve readily in acids 
with the evolution of hydrogen. It dissolves most readily in 
nitric acid, chiefly with the evolution of nitric oxide: 

3Cu + 8HNO3 = 3Cu(N0 3 ) 2 + 4H 2 + 2NO. 

With hot concentrated sulphuric acid, sulphur dioxide is 
evolved : 

Cu + 2H-S04 = CuS0 4 + 2H 2 + S0 2 . 



152 COPPER 

Dilute hydrochloric and sulphuric acids are without 
action upon copper when air is excluded, but slowly attack 
it in the presence of air or a catalytic agent, such as platinum. 
Finely divided copper is soluble in boiling concentrated 
hydrochloric acid. In the presence of air, copper is acted 
upon by ammonia, forming a deep blue solution. Water 
dissolves copper from a polished copper surface and it is 
found that the water has been sterilized by the copper in 
solution. 

Compounds. — Copper forms two classes of compounds: 
cuprous with a valency of one and cupric having a valency 
of two. The cuprous compounds are very unstable. 

Cuprous oxide, Cu 2 0, occurs native as red copper ore. It 
may be prepared in the wet way by heating cuprous chloride 
with sodium carbonate in a crucible. Cuprous oxide fuses 
at red heat and when melted with glass imparts a rich ruby 
red color. Cuprous oxide occurs in the rare mineral tenorite. 
It is formed when copper is heated in air or oxygen. This 
compound of copper is extensively used in chemistry because 
of its oxidizing power. In dentistry it is used in black copper 
cements. Cupric hydroxide is a pale blue precipitate formed 
when sodium or potassium hydroxides are added to a solution 
of a copper salt. If the precipitate is boiled, a black basic 
oxide of copper is formed. If ammonium hydroxide is added 
to a soluble copper salt the hydroxide is first precipitated; 
this dissolves in an excess of ammonium hydroxide, result- 
ing in the production of a blue solution, copper sulphate; 
blue vitriol is formed by dissolving the metal or its oxide in 
sulphuric acid. This salt is used in the preparation of voltaic 
cells, and is also used in medicine. 

Sulphides. — Two sulphides are known: cuprous, Cu 2 S, 
and cupric, CuS. Cuprous sulphide occurs in nature as 
copper glance, in the form of gray metallic-looking rhombic 
crystals. It may be prepared in the dry way by burning 
copper in sulphur vapor. Cupric sulphide occurs in nature 
as indigo-copper. It may be prepared in the dry way by 
heating copper or cuprous sulphide with sulphur to a tem- 
perature not above 114°; so obtained the compound is 



ALLOYS 153 

blue. In the wet way hydrogen sulphide precipitates it 
from solutions of cupric salts; it is a black precipitate. 

Alloys. — Copper amalgam was used to a considerable 
extent at one time in dentistry; however, at the present 
time it has gone into disuse and only occasionally it is 
of service to the dentist. It may be prepared by pouring 
pure mercury into a beaker containing copper sulphate and 
then stirring with an iron rod. An amalgam known as 
Sullivan's amalgam is prepared as follows: pure copper is 
obtained in a finely divided state by boiling a concentrated 
solution of copper sulphate with distilled zinc until the color 
of the salt disappears, when the zinc is removed. The 
pulverulent mass of copper in the bottom of the vessel is 
washed with dilute sulphuric acid and then with distilled 
water and dried. The copper is then treated with a solution 
of mercuric nitrate until it becomes coated with mercury. 
The mercury is then added to the extent of about twice the 
weight of copper. It is then rolled into small lozenge-shaped 
pieces which become quite hard. This amalgam possesses 
the property of softening with heat and again hardening, 
and when employed as a filling material one of the lozenge- 
shaped pieces is placed in a small iron spoon and heated 
over the flame of a spirit lamp until small globules of mercury 
are driven to the surface, when it is placed in a small glass 
or porcelain mortar and rubbed into a smooth paste. Some 
recommend washing, with a weak solution of sulphuric acid, 
or soap and water, and lastly with clean water alone, to 
remove the last traces of either acid or soap", and finally 
squeezing through chamois-leather, to exclude surplus of 
mercury, when it is ready to be introduced into the cavity. 
It requires several hours to harden. Mr. Fletcher says of 
this amalgam that " it is an absolutely permanent filling, as 
the copper salts permeate and perfectly preserve the tooth." 
It is said to be quite insoluble in the mouth. It, however, 
becomes intensely black, and imparts a most objectionable 
stain to the teeth. 

Copper and iron form no true alloy, but when these two 
metals are mixed the copper is found irregularly distributed 
throughout the mixture. 



154 COPPER 

Tin alloys with copper and diminishes the malleability; 
this effect is produced even when tin is present to the extent 
of 1 per cent, or over. 

Zinc and copper, forming brass, diminishes the malleability 
when hot. 

Lead and copper are miscible in all proportions, but the 
greater part of the lead may be liquated from the alloy by 
gentle heating. In small quantities it does not interfere 
with malleability. 

Bismuth renders copper unworkable and a few thousandths 
of 1 per cent, interferes with its conductivity. 

Silver and copper are alloyed for the purpose of coinage. 

Gold and copper are also used for coinage; the copper is 
added to increase the hardness of the gold. 

Platinum and palladium alloy with copper in certain 
proportions; the first forms an alloy resembling gold in 
color, while the latter resembles brass. 

Aluminum bronze consisting of aluminum and copper, 
and containing from 1 to 10 per cent, aluminum, resembles 
gold in color and is very resistant to the action of solvents. 
It is also malleable and ductile. This alloy has been used 
for orthodontic appliances. 

The following are among the most important alloys of 
commerce : 

English brass copper, 2 parts; zinc, 1 part. 

Dutch brass (Tombac) . . copper, 5 parts; zinc, 1 part. 

Muntz metal copper, 3 parts; zinc, 1 part. 

Gun metal copper, 9 parts; tin, 1 part. 

Aluminum bronze . . . copper, 9 parts; aluminum, 1 part. 

Resume. 

Symbol, Cu. Boiling point, 2310° C. 

Valency, I or II. Specific gravity, 8.8 to 8.9. 

Atomic weight, 63.57. Crystalline form, isometric. 

Melting point, 1150° C. Conductivity of electricity, 2d. 

Specific heat, 0.0968. Conductivity of heat, 2d. 

Malleability, 4th. Coefficient of expansion, 
Tenacity, 2d. 0.000017182. 

Color, pink. Ductility, 5th. 



CHAPTER XII. 
CADMIUM. 

Symbol, Cd. Atomic weight, 112.4. 

Occurrence. — The only cadmium mineral is the sulphide 
greenockite (CdS). The principal source is from zinc ores 
which contain from 1 to 3 per cent.; and in the process of 
extracting zinc the cadmium is obtained in the first portions 
of the product of the distillation, partly as metal and partly 
as oxide. 

Reduction. — The crude product as obtained from the calci- 
nation, reduction, and distillation of zinc ores, is dissolved in 
dilute sulphuric or hydrochloric acid and the cadmium pre- 
cipitated as the sulphide with hydrogen sulphide. The 
cadmium sulphide is then dissolved in strong hydrochloric 
acid and precipitated as carbonate, by means of ammonium 
carbonate. The washed and ctried carbonate is first converted 
into the oxide, and finally mixed with charcoal and distilled. 
A second process consists in redistilling the crude metal 
obtained from the distillation of zinc, and then dissolving 
in hydrochloric acid, then precipitating from solution by 
means of zinc plates. 

CdCl 2 + H 2 + Zn = Cd + ZnCl 2 . 

Properties. — Specific gravity, liquid, 7.986; cooled, 8.67; 
hammered, 8.6944; melting point, 320.6°C, 608° R; boiling 
point between 772° and 763° C; specific heat, 0.0567. It 
is a bluish-white metal resembling zinc in appearance but 
much more malleable and ductile. It tarnishes superficially 
on exposure to air, and when strongly heated burns with the 
formation of a brown vapor of cadmium oxide, CdO. Cad- 
mium is a soft metal, harder than lead, but softer than tin 
or zinc. Conductivity, somewhat less than zinc. More 
tenacious than tin. At a temperature of 80° C. cadmium 
becomes very brittle, and upon bending it emits a sound 



156 CADMIUM 

similar to the cry of tin. It may be distilled in a current of 
hydrogen above 800° , forming silver- white crystals belonging 
to the regular system. Cadmium is less electropositive than 
zinc, and is precipitated in the metallic condition, from its 
solutions, by that metal. It precipitates Au, Pt, Ag, Hg, 
Bi, Cu, Pb, Sn, and Co, and is precipitated itself by zinc, 
Mg, and Al. 

Solubilities. — Cadmium dissolves slowly in hot, moderately 
dilute hydrochloric and sulphuric acids, with the evolution 
of hydrogen: 

Cd + 2HC1 = CdCl 2 + H 2 
Cd + H 2 S0 4 = CdS0 4 + H 2 . 

Alkalies are said to dissolve it. Cadmium is readily soluble 
in nitric acid with generation of nitrogen oxides. Cadmium 
oxide, formed when cadmium burns in air, is brown in color, 
and may also be obtained by heating the nitrate or carbonate. 
Cadmium and silver are miscible in all proportions and three 
compounds are formed. The fusing point of cadmium is 
only slightly raised by the addition of small quantities of 
silver, according to the experiments of Petrenko and Fedorov. 
Uses.- — Cadmium is used in low fusing alloys; unlike 
bismuth, the cadmium alloys are not brittle. Some of these 
alloys fuse below the boiling point of water; they may be 
hammered or rolled but are not so crystalline in structure 
as the bismuth alloys. 





Cd. 


Pb. 


Sn. 


Bi. 


Melting points. 


Wood's metal . 


. 2 


4 


2 


5 


160° F., 71° C. 


Lipowitz 


. 3 


8 


4 


15 


158° F., 65° C. 


Molyneaux's alloy 


. 2 


3 


2 


5 


60° C. 


Crouse's alloy . 


. 1 


5 


3 


8 


79° C. 


Lichtenberg's alloy 


. 2 


13 


7 


7 


75° C. 



Resume. 

Symbol, Cd. Boiling point, 756° C. 

Valency, II. Specific gravity, 8.6. 

Atomic weight, 112.4. Chief ore, greenockite. 

Melting point, 320.6° C. Conductivity of electricity, 159. 

Specific heat, 0.0567. Coefficient of expansion, 
Malleability, 5th. 0.000012. 

Color, bluish white. Ductility, 11 th. 



CHAPTER XIII. 
ANTIMONY. 

Symbol, Sb (stibium). Atomic weight, 120.4. 

Historical. — Antimony has been known from antiquity. 
Jeremiah speaks of it (Stibick stone), being used to blacken 
the eyebrows, or as a cosmetic. The Romans used a chalice 
lined with antimony, placing sour wine into it and allowing 
it to stand overnight. The contents was drunk after a 
night of debauching and the tartar emetic formed would 
produce its characteristic effects, relieving the distress of the 
person partaking of the draught. 

Occurrence. — Lead ores sometimes contain antimony. 
The sulphide stibnite, Sb 2 S 3 , is the chief ore. It also occurs 
as the native metal containing arsenic, iron and silver as 
impurities. There are also natural occurring oxides, valen- 
tinite, Sb 2 3 , antimony ochre, Sb 2 4 , but they are found only 
in small quantities. France, Italy, Mexico and Japan are 
the chief producers of antimony. 

Reduction. — Antimony may be reduced from the sulphide 
by one of the following processes: 

1. The crushed ore is heated in plumbago crucibles with 
scrap iron. The mass melts and the sulphur combines with 
the iron, forming iron sulphide and liberating the antimony 
which settles beneath: 

Sb 2 S 3 + 3Fe = 2 Sb + 3FeS. 

2. The crude antimony is freed from earthy impurities 
by melting, the antimony sulphide is then drawn off from 
the impurities. The purified ore is mixed with about one-half 
its weight of charcoal, to prevent caking, and carefully roasted. 
The antimony is partially converted into the oxide, a portion 
of which volatilizes and collects in the flues. The arsenic 
present is also oxidized and collects with the oxide of anti- 
mony, while the sulphur passes off as a sulphur dioxide. The 



158 ANTIMONY 

antimony ash remaining in the furnace, consisting of the 
oxide and unchanged antimony sulphide, is mixed with char- 
coal and sodium carbonate and heated to redness in a crucible. 

1. Sb 2 4 + 4C = 4CO + 2Sb 

2. Na 2 C0 3 + 2C = 3CO + 2Na 

3. Sb 2 S 3 + 6Na = 3Na 2 S + 2Sb. 

The metal as obtained by this process must be subsequently 
refined. The impurities commonly present are sulphur, 
copper, iron, arsenic, silver and gold. The metal may be 
refined by fusing with sodium carbonate and a little sulphide 
of antimony, followed by two fusions with sodium carbonate 
alone. Liebig's process consists in fusing the impure anti- 
mony with sodium carbonate, potassium carbonate and a 
little antimony sulphide. 

Properties. — A very brittle tin-white metal, usually 
massive, with fine, granular, steel-like texture. It is very low 
in malleability, tenacity, and ductility; hardness about 3 to 
3.5; specific gravity, 6.5 to 6.7; melting point, 425° C, 
797° F.; boiling point, between 1090° and 1450° C, specific 
heat, 0.0513. It is but little tarnished in dry air and oxidizes 
but slowly in moist air, forming a mixture of antimonous 
oxide and antimony which is of a blackish-gray color. At 
red heat it burns in air with incandescence, forming white 
antimonous oxide. In the act of solidification, antimony 
expands; it imparts this property to its alloys, thus giving 
to them the valuable property of taking very fine and sharp 
lines in casting. It is a very poor conductor of heat and 
electricity and is a diamagnetic in its behavior toward the 
magnet. The powdered metal unites with chlorine gas, 
taking fire spontaneously and forms the trichloride SbCl 3 . 
Antimony may be obtained in the amorphous form by the 
electrolysis of a solution of tartar emetic. This form of 
antimony has the appearance of a smooth, polished rod of 
graphite. Amorphous antimony is very unstable and the 
slightest disturbance will cause it to change, with explosive 
violence, to the crystalline form. 

Oxides. — Antimony forms three oxides: Sb 2 3 , Sb 2 4 , 
and Sb 2 5 . 



SOLVENTS 159 

Antimonous oxide, Sb 2 3 , is formed: (1) when dilute nitric 
acid acts upon Sb; (2) by treating antimonous chloride, 
SbCl 3 , with Na 2 C0 3 or NH 4 OH; (3) by heating Sb 2 4 or 
Sb 2 05 to 800°. It is a white powder which turns yellow on 
heating and again becomes white upon cooling. It melts at 
red heat, becomes crystalline upon cooling. Antimonous 
oxide sometimes acts as an acid, with sodium hydroxide it 
reacts as follows: 

Sb 2 3 + 2NaOH = 2NaSb0 2 + H 2 0. 

But under most conditions it acts as a basic oxide. 

Antimony tetroxide, Sb 2 4 , is formed when antimony burns 
in air. It may be prepared by strongly heating antimony 
pentoxide ; 

2Sb 2 5 = 2Sb 2 4 + 2 . 

Antimony tetroxide is a white, non-volatile powder which 
is insoluble in water. It is decomposed by boiling hydrogen 
potassium tartrate, cream of tartar forming tartar emetic: 

HK(C4H 4 6 ) + Sb 2 4 = (SbO)K(C 4 H 4 6 ) + HSb0 3 . 

Antimony pentoxide, Sb 2 05, is obtained by treating anti- 
mony with strong nitric acid and heating the antimonous 
acid formed to 275°. It is a straw-colored powder, insoluble 
in water; when heated to 300° it is converted into Sb 2 4 . 
It possesses feeble acid properties; when fused with sodium 
carbonate, sodium metantimonate is formed: 

Sb 2 5 + Na 2 C0 3 = C0 2 + 2NaSb0 3 . 

Antimony salts in solution readily form basic salts and are 
thus precipitated from solution; however, in the presence of 
acids this reaction will not occur. 

SbCl 3 + H 2 = SbOCl + 2HC1. 

Solvents. — Dilute hydrochloric and sulphuric acid are with- 
out action upon antimony. The concentrated acids convert 
it into the sulphate and chloride respectively. 

2Sb + 6H2SO4 = 3S0 2 + 6H 2 + Sb 2 (S0 4 ) 3 . 
2Sb + 6HC1 = 2SbCl 3 + 3H 2 . 

Dilute nitric acid attacks antimony with the formation of 
Sb 2 3 or a compound of the oxide with nitrogen pentoxide: 

Sb 2 3( 3N 2 6 . 



160 ANTIMONY 

Concentrated nitric acid oxidizes the antimony chiefly 
into the tetr oxide and pentoxide. 

2Sb + 2HN0 3 = Sb 2 3 + H 2 + 2NO. 
6Sb + lOHNOs = 3Sb 2 5 + 5H 2 + 10NO. 
6Sb + 8HNO3 = 3Sb 2 4 + 4H 2 + 8NO. 

Aqua regia attacks antimony with the formation of the 
trichloride SbCl 3 , but if sufficient nitric acid be present this 
is rapidly changed to antimony pentachloride, SbCl 5 ; how- 
ever, if too much nitric acid is present, the corresponding 
oxides are formed. 

Alloys of Antimony. — Antimony increases the hardness of 
metals when alloyed with them. It causes expansion in most 
alloys and is used in type metal. With the noble metals it 
renders them brittle and thus destroys their malleability 
and ductility. 

Amalgam of antimony is soft and readily decomposes. 

Gold.— Antimony destroys the malleability of gold. 

Tin. — Antimony increases the hardness of tin but renders 
it brittle. 

Type metal consists of lead, 50; antimony, 25; tin, 25. 
Copper is sometimes added to some varieties. 

Antifriction metal is made by alloying copper, antimony, 
and tin in various proportions. Other varieties contain lead, 
antimony and tin. 

Britannia metal is an alloy of tin, antimony, copper, zinc, 
and bismuth; it is used in making spoons resembling silver. 



Resume. 

Valency, III or V. Ductility, brittle. 

Atomic weight, 120.2. Chief ore, stibnite. 

Melting point, 425° to 632° C. Crystalline form, rhombo- 
Boiling point, 1440° C. hedral. 

Specific heat, 0.0513. Conductivity of heat, 40. 

Color, bluish white. Conductivity of electricity, 4.5. 

Specific gravity, 6.8. Coefficient of expansion, 
Malleability, brittle. 0.000017. 



CHAPTER XIV. 
TIN. 

Symbol, Sn (stannum). Atomic weight, 119. 

Occurrence. — Tin occurs as the oxide cassiterite or tin- 
stone, Sn0 2 , which is the principal ore. It is also found in 
small quantities as the sulphide, in the mineral stannite 
(CuSnFe)S. The ores of this metal are found in primitive 
rocks, generally in granite either in veins or beds, and often 
associated with copper and iron pyrites. The East Indian 
settlements of Malacca, Banca and Belitong are the greatest 
producers of tin-stone. It is also found in Australia, England, 
Mexico and various localities in the United States. 

Historical. — Tin has been known from the earliest of times, 
being used in the construction of bronze. The Phoenicians 
traded with England for this article for more than 1100 years 
before the Christian Era. 

Reduction. — In the reduction of tin-stone the process 
ordinarily consists of three operations, namely: (1) Calcining; 
(2) washing; (3) reducing or smelting. If the ore is free from 
impurities as it is occasionally found (stream-tin), it may be 
smelted at once. The ore is washed to free it from earthy 
matters, then finely crushed. It is next placed in a reverbera- 
tory furnace and calcined. Sulphur and arsenic pass off as 
sulphur dioxide and arsenious oxide, and the arsenic deposits 
in the flues. The iron and copper are oxidized to oxide and 
sulphate. The calcined ore is next washed, whereby copper 
sulphate is dissolved and the iron oxide and other lighter 
matters are removed. The purified ore is then mixed with 
powdered coal and smelted in a reverberatory furnace: 

Sn0 2 + 2C = 2CO + Sn. 

The tin usually contains lead, iron, arsenic, antimony and 
copper. The metal so obtained is purified by first heating 
11 



162 ■ TIN 

it upon the hearth of a similar furnace until the more readily 
fusible tin melts and flows away from the associated alloys; 
then by stirring into the molten tin mats of green wood, 
which results in the separation of a dross carrying with it the 
impurities. 

Properties. — Tin is a white metal and is not acted upon by 
air. It is a soft metal and can be readily cut with a knife; 
it is harder than lead, but softer than zinc. It is both ductile 
and" malleable at ordinary temperatures and at 100° C. it 
can be drawn into an extremely fine wire. At a temperature 
just below its fusing point (232°), it becomes very brittle 
and may be powdered. Tin can exist in two forms, white tin, 
as we ordinarily know it, and a gray form. Gray tin is formed 
when white tin is exposed to a low degree of temperature. 
Below 20° C. the gray is the stable form of tin. It is reported 
that some of the sufferings of the Scott Exploring Expedition 
to the South Pole, in the last few years, was due to the 
crystallization (formation of gray tin) of the tin gasoline 
tanks. The crystalline nature of tin may be observed by 
etching the surface of it with dilute hydrochloric or sulphuric 
acids. When bent, tin emits a crackling sound, called the cry 
of tin, and if the bending is continued for a few times, the 
surface of the tin becomes heated; the heat and sound are 
caused by the movement of the crystalline particles. Tin 
boils at about 2270°; it is a poor conductor of electricity. 
Hydrogen sulphide does not attack tin at ordinary tempera- 
ture, consequently tinned surfaces are more permanent than 
silvered ones. When strongly heated, tin takes fire and 
burns, forming stannic oxide, Sn0 2 . At red heat it decom- 
poses steam with the formation of hydrogen. Tin forms 
two oxides, stannous and stannic. Stannous oxide, SnO, is 
prepared by treating a solution of stannous chloride with 
potassium carbonate, when the hydrated oxide (SnO, H 2 0) 
is precipitated. The hydrated oxide is washed with boiling 
water, air being excluded, and then dryed at 80° or lower. 
It is a black or bluish-black powder and when heated in air 
becomes incandescent, burning to the dioxide. 

Stannic oxide, Sn0 2 , exists in two forms, crystalline and 



SOLUBILITY 163 

amorphous. The natural occurring tin-stone is crystalline 
and that prepared artificially is amorphous. The amorphous 
stannic oxide may be prepared by a number of methods: 
when tin is heated to white heat; treating stannic salts with 
alkali carbonates and igniting; and when tin is oxidized 
with nitric acid; are a few methods that may be mentioned. 
Stannic acid is both acid and basic in properties and forms 
stannic salts, exhibiting basic properties, and in stannates, 
its acid properties. Stannic oxide is insoluble in acids 
and alkalies; but is attacked when fused with potassium 
hydroxide, forming potassium stannate, Iv 2 Sn0 3 . Stannic 
oxide is used as a polishing powder and is known as "putty 
powder." 

Tin forms two acids, stannic, H 2 Sn0 3 , and metastannic acid, 
HioSn 5 Oi5, or (H 2 Sn0 3 )5. The latter is formed as an insoluble 
powder when tin is treated with strong nitric acid. Stannous 
chloride, formed by dissolving tin in hydrochloric acid, is 
a valuable compound used in tests for certain metals and also 
as a reducing agent in- the wet way. In an analysis of an iron 
ore, the iron must be in the ferrous condition; stannous 
chloride is the reagent used to bring about the reduction. It 
is also used to identify mercury in solution, reducing soluble 
mercuric chloride to the insoluble mercurous chloride. 

HgCl 2 + SnCh = Hg 2 Cl 2 + SnCU. 

Solubility. — Nitric acid attacks tin, the very dilute acid 
forming stannous nitrate, but the concentrated acids 
precipitate metastannic acid which is insoluble in acids. If 
alloys containing tin are "pickled" in nitric acid, that is, 
if the alloy be heated for the purpose of annealing and then 
dipped into the acid to remove oxides formed by heating, 
a bright metallic surface will not be produced, instead, the 
surface will assume a dirty appearance, due to the formation 
of stannic oxide. When concentrated nitric acid (sp. gr., 
1.24) acts upon tin a rather violent action takes place; how- 
ever, the strongest nitric acid (sp. gr., 1.5) is said to be without 
action upon it. Hydrochloric acid and sulphuric acid both 
dissolve tin and the products formed with sulphuric acid 



164 TIN 

depend upon the strength of the acid. Potassium hydroxide 
in the presence of air slowly attacks tin. 

Uses. — Tin is used in the process of tinning, which consists 
of dipping sheet iron into a vessel of molten tin, thus giving 
the iron a superficial coating to increase the resistance of the 
iron to solvents and oxidation. In dentistry tin is used as 
tin foil in the vulcanization of rubber dentures. The tin foil 
is adapted to the surface of the plaster model and the den- 
ture upon removal from the flask may be separated from 
the tin foil either by mechanical means or by simply using a 
dilute solution of hydrochloric acid. The palatine portion 
of the upper denture, and also the portion of the lower denture 
covering the ridge, will be found to have a polished surface. 
When tin foil is not used it frequently happens that the 
plaster adheres very tenaciously to these portions of a denture, 
and any attempts to polish may ruin the piece of work. 
Tin foil is also used to reproduce the rugae upon the lingual 
aspect of an upper denture. Again, tin foil is used as a filling 
material, and also with gold as a tin-gold filling. It is worked 
in the same manner as the so-called non-cohesive gold foils, 
i. e., by a process of wedging. In the tin-gold fillings the 
tin foil is used in some cases to restore the tooth substance 
below the gingival margin and the filling is then finished with 
gold. In other cases it has been used to facilitate the intro- 
duction of gold, as in large cavities; in this instance it lessens 
the time it would take to introduce all gold; this saves a 
great amount of labor for the dentist and is not so fatiguing 
to the patient. Tin-and-gold fillings in some cases turn black, 
and resemble amalgam fillings; the theory has been advanced 
that galvanic action is the cause of this discoloration. In 
the past few years a preparation supposed to be pure tin 
in a shredded form was placed upon the market; this material 
is said to be cohesive and may be worked like cohesive gold. 
It was intended to be used as a filling material following the 
same precautions and technic as if it were gold. Because of 
its low conductivity of heat, non-irritating, and property 
of not forming compounds which would discolor tooth struc- 
tures, tin has various other uses, among which might be 



LEAD AND TIN 165 

mentioned the following: As a non-conducting material 
in sensitive cavities, and in case of a perforated root, to 
prevent the root canal filling from being forced into the 
surrounding soft tissues. 

Dental rubber for weighted lower dentures contains 
metallic tin as the weighting material. This rubber is 
sometimes used when there is considerable loss of tissue and 
the lower denture demands a very thick rubber restoration; 
the tin reduces the bulk of rubber and aids in the overcoming 
of porosity of the rubber during vulcanization. Block-tin 
is sometimes used in cheoplastic operations for the con- 
struction of lower dentures. 

Alloys. — Tin and mercury amalgamate readily and chemi- 
cal compounds having various formulas are supposed to be 
formed. Silver and tin form an alloy which is harder than 
tin. Dr. Bean's alloy, containing ninety-five parts tin and 
Hve parts silver, is used in cheoplastic operations in which 
the alloy is cast directly upon the vulcanite teeth. 

In cheoplastic operation a wax model of the parts to be 
cast is made; this is invested in a suitable flask, and when the 
investment has hardened, the wax is removed by separating 
the flask and using hot water. The flask is then bolted 
together and the joints made tight with fresh investing 
materials, and the piece thoroughly dried. Molten metal is 
poured into the flask through the pouring gates, and upon 
cooling the piece is removed from the flask and receives 
mechanical treatment, such as filing and polishing. In 
some cases the metal may be poured directly against the 
vulcanite teeth, and the complete restoration of the lost 
parts made of metal, while in other cases simply a metallic 
base is cast and the teeth attached by the use of vulcanite 
rubber. Platinum and tin form an alloy which fuses at a 
comparatively low temperature. This alloy is hard and 
brittle. 

Palladium also forms a brittle alloy with tin. 

Lead and Tin. — These two metals readily alloy and form 
the so-called soft solders. The following is a list of soft 
solders: 



166 TIN 

Tin. Lead. Bismuth. Fusing point. 

Soft, course .... 1 2 '. . 441° F. 

Soft, fine 2 1 .. 475° F. 

Soft, fusible ..... 2 1 1 

The following is a list of solders and flux used in soldering 
some of the metals: 

Materials to be soldered. Solder. Flux. 

Tin plate Soft, coarse or fine Rosin or zinc chloride. 

Lead Soft or coarse Rosin. 

Brass, copper, iron and zinc Soft or coarse Zinc chloride. 

Tin is used as a constituent of low fusing alloys. 

Dr. C. M. Richmond's alloy fuses at 150° F., and may be 
poured into a plaster impression without generating steam. 
The formula of this alloy is as follows: 

Tin 20 parts by weight 

Lead 19 " 

Cadmium 13 " 

Bismuth 48 " 

The following alloys may also be used: 

Tin. Lead. Bismuth. Melting point alloy. 

12 2 236° F. 

5 3 3 202° F. 

3 5 8 197° F. 

Babbitt metal, named after Isaac Babbitt, of Boston, is an 
alloy consisting of nine parts tin and ten parts copper, used 
for journal boxes. Many modifications have been made in 
this alloy, but the term is still applied to any white alloy 
employed in the construction of bearings, to distinguish it 
from the bronzes and brasses. Alloys used for this same 
purpose and known as antifriction metals, for the most part 
consist of lead, antimony, and tin. Dr. Fletcher recommends 
an alloy of copper, 4 pounds; Banca tin, 96 pounds; regulus 
antimony, 8 pounds. This alloy is said to be nearly as hard 
as zinc, while its shrinkage is much less. These qualities, 
together with the low temperature at which it fuses, entitle 
it to a place in the dental laboratory for the preparation of 
dies and counter-dies. 

Dr. L. P. Haskell recommends the formula: tin, 72.72; 
copper, 9.09; antimony, 18.18. 



LEAD AND TIN 167 

Bronze is an alloy of copper and tin, and sometimes zinc. 
It is affected by changes of temperature in a manner precisely 
the reverse of that in which steel is affected, becoming soft 
and malleable when quickly cooled, and hard and brittle 
when allowed to cool slowly. The art of making bronze 
was practised before any knowledge of the working of iron 
existed, and it was used at a very early period in the manu- 
facture of weapons. 

Commercial tin is liable to contain minute quantities of 
lead, iron, copper, arsenic, antimony bismuth, etc. Pure tin 
may be precipitated in crystals by the feeble galvanic current 
excited by immersing a plate of tin in a strong solution of 
stannous chloride. Water is carefully poured on so as not to 
disturb the layer of tin solution. The pure metal will be 
deposited on the bar of tin at the point of junction of the 
water and the metallic solution. 

Resume. 

Symbol, Sn. Chief ore, tin-stone, cas- 

Valency, II or IV. siterite. 

Atomic weight, 119. Conductivity of heat, 145 

Melting point, 232° C. or 6th. 

Specific heat, 0.0555. Conductivity of electricity, 

Boiling point, 2270° C. 12.22. 

Color, white. Coefficient of expansion, 

Malleability, 3d. 0.00002173. 

Specific gravity, 7.29. Ductility, 7th. 

Crystalline form, quadratic Tenacity, 7th. 



CHAPTER XV. 
GOLD. 

Symbol, Au (aurum). Atomic weight, 197.2. 

Occurrence. — Gold occurs in nature in the native state. It 
is found present in small quantities in certain sulphides and 
also in combination with tellurium. 

Native gold with comparatively few exceptions is found in 
veins of quartz. The gold occurs in the quartz, irregularly 
distributed in strings, scales, plates and in masses. As the 
result of erosive changes occurring in the vein formation 
gold is also found in the gravel or sands of rivers and valleys 
and these are known as alluvial deposits. Gold as it occurs 
in vein formation is sometimes spoken of as reef-gold. 

Alluvial gold occurs as dust, grains and larger pieces 
(nuggets) in alluvial deposits, which form beds of sand or 
gravel, either upon the surface, called shallow placers, or at 
greater or less depth (deep placers) , which have been produced 
by the destruction of the gold-bearing deposits. 

Gold nuggets of enormous size have been found at various 
times, the Australian gold region has yielded two nuggets, 
one weighing 184 and another 190 pounds. Eggleston states 
that the gravels of California have yielded a nugget weighing 
2250 ounces troy (153 pounds avoirdupois). 

Native gold ordinarily contains up to 16 per cent, of silver. 
The purest which has been described is that obtained from 
Mount Morgan in Queensland, which has yielded 99.7 to 
99.8 per cent, of gold, the remainder being copper, iron and 
only a trace of silver. The native metal usually contains 
silver, copper, bismuth, rhodium, or palladium. 

According to Wagner the following is a list of analyses of 
native golds obtained from various sources: 



OCCURRENCE 169 

Transyl- 
vania. S. America. Siberia. California. Australia. 

Gold .... 64.77 88.04 86.5 90.60 99.20 to 95.7 

Silver .... 35.23 11.96 13.2 10.06 0.43 to 3.8 

Iron and other metals . . .. 0.3 0.34 0.28 to 0.2 

Small quantities of native amalgam have also been found. 

Sulphides Containing Gold. — Pyrite sometimes contains 
gold distributed invisibly through it; the ore, auriferous 
pyrite is an important source of gold and ranks next to the 
native metal as a source of gold. 

Arsenopyrite is mined in Ontario for the gold which it 
contains. 

Chalcopyrite, the chief working ore of copper, may also 
contain gold and silver, and special metallurgical processes 
must be made use of for the removal of the metals from 
copper. 

Marcasite, galena and sphalerite also frequently contain 
gold. 

Minerals of Gold. — The tellurides are possibly the only 
compounds of gold occurring in nature to any great extent. 
Sylvanite, (AuAg)Te 2 , contains about 24 to 26 per cent, of 
gold. This mineral is found in Transylvania, California and 
Colorado. Krennerite has the same formula as sylvanite. 

Calaverite, (AuAg)Te 2 , with Au contains about 42 per cent, 
of gold. 

Nagyagite or foliated tellurium, (Pb, Au) 2 (STeSb) 3 , contains 
only about 5 to 9 per cent, of gold. The tellurides are the 
principle gold-bearing ores of Colorado, and to show the 
importance of these ores, Colorado in 1913 produced 878,021 
ounces of gold having a valuation of $18,148,711.27. 

In December, 1914, a deposit of calaverite and sylvanite 
was discovered in the Cresson mine located at Cripple Creek, 
Col., at a depth of 1265 feet. The amount of gold that the 
deposit will produce has not been estimated ; however, it is 
considered the greatest strike of its kind ever made. Gold 
is a universally occurring element, small quantities being 
present in sands and also surface and sea waters; however, 
it is present in such small quantities that it cannot be profit- 
ably recovered. The richest sources, and the value of the 



170 GOLD 

gold recovered in various localities for the year 1914, are 
as follows: 



Cape Colony, etc. / 
United States 
Russia .... 
Australia 
Balance of the world 



Oz. fine. Value. 

8,395,964 $173,560,000 

4,573,976 94,531,800 

1,382,897 28,587,000 

1,232,973 25,487,800 
6,453.728 



The following represents the production in the United 
States for 1914 from the three principal sources: 

Oz. fine. Value. 

California ..... 1,028,061 $21,251,900 

Colorado ..... 962,779 19,902,400 

Alaska ....'.. 800,471 16,547,200 

Historical. — Gold has been known and used by mankind 
from the earliest of times. It has been made use of for 
ornamental purposes and as a circulating medium, because 
of its scarcity, beautiful color and also its resistance to 
corrosive influences. Gold has played a very important 
part in the development of the human race, politically, and 
also scientifically. 

The history of America shows that the finding of gold was 
ever before the minds of the early explorers. Columbus, in 
his second voyage in the year 1493, found Jamaica and the 
other islands, and sought for gold but was not successful. 
Cortez in his search for gold was led to Mexico and his 
exploits to obtain this metal is a good illustration of the 
influence gold has had upon mankind. About $17,500,000 
worth of gold was a little later seized by the Spaniards from 
the Incas in Peru. De Sota and De Coronado, both in search 
of gold, were led to regions unexplored. These few illus- 
trations show how the search for gold caused the exploration 
of the various parts of the western hemisphere; in fact, as 
soon as a new territory had been discovered in the past, one 
of the first inducements to settlers was the thought of the 
discovery of gold. The famous gold fever of "49", causing 
trains of prospectors to cross the prairies and the intense 
hardships endured in their attempt to reach California 



THE EXTRACTIOX OF GOLD 171 

and her gold fields, and later the rush to Alaska, tends to 
show how this metal has caused new districts to be peopled 
and also its influences upon humanity. 

It has caused the conquest of nations, the enlargement of 
dominions, the development of industry in all its branches, 
and on the other hand, every crime conceivable has been 
committed for its possession. 

The search for gold has led to the development of the 
various sciences. In the olden times great efforts were 
expended by the alchemists to find a simple method of pro- 
ducing the metal, thus causing the development of chemistry 
and its allied sciences. At the present time it is one of the 
prime objects of the metallurgical world to produce this 
metal at the least possible expense. The effect is that metal- 
lurgy has received one of its principal stimuli from gold. 

The Extraction of Gold. — Gold is obtained from its ores by 
metallurgical processes or by direct washing. 

Direct Washing Process. — There are three methods of 
direct washing: (1) Placer mining. (2) Hydraulic mining. 
(3) Dredging. 

Placer Mining. — Placer mining is at the present time rarely 
used because of the heavy loss of gold entailed by its use; 
this may amount to 50 per cent, of gold present in the pay 
dirt. At one time the prospectors used the so-called pan. 
In panning, a black sheet-iron, sheet-tin or wooden pan, 
about 16 inches in diameter and 2 inches deep, was used. 
The pan was filled about two-thirds full of pay dirt and then 
held in a stream or pool of water. The pan was given a 
twisting motion and the heavier particles of gold descended 
to the bottom of the pan. The cradle and the Long Tom 
are other devices for carrying on this same process on a 
larger scale. At the present time they are used to some extent 
by the Chinese of California, in washing tailings which have 
already been washed several times. With the cradle a man 
may wash \\ cubic yards of gold-bearing sand in a day, 
while with the Long Tom two men can wash about 8 cubic 
yards. The loss of gold by these methods is also very 
heavy. 



172 GOLD 

The sluice is the appliance mostly used in the United 
States in the washing process. It consists of a series of 
troughs or boxes, about 1 foot 4 inches wide and 9 inches 
deep. Each box is 12 feet long and is so connected as to form 
long troughs, inclined about 8 to 20 inches to each 12-foot 
box. They are fitted with wooden slats or riffles, which are 
wedged into place, either longitudinally or transversely, to 
assist in the breaking up of the earthy matter. At certain 
points under currents are placed to separate the coarser 
pebbles. These are formed by replacing the bottom of a 
sluice by a grating known as a grizzly and leaving the end of 
the box open. Underneath the grating there is a trough at 
right angles to the main, leading to other sluices parallel 
to the first. The finer and heavier gold-laden material passes 
through the grating and is carried to the second line of sluices 
which are much wider and not so deep; this gives the gold 
an opportunity to settle in the sluices. Mercury is generally 
sprinkled into the cross riffles and amalgamates with the 
gold. 

Hydraulic Method. — Water is forced into the gold-bearing 
gravels under high pressure and then conveys the gravel 
into long sluices. The gold is taken up by mercury, and the 
amalgam submitted to dry methods of refining. 

Dredging. — Dredging the river beds for gold has attracted 
some attention within recent years. Some of the dredge 
buckets used have a capacity of 16 cubic feet and dredge 
and wash 300,000 cubic yards at a cost of less than three 
cents a cubic yard. The drawback to this industry is the 
high cost of electricity. Fig. 48 illustrates a dredge in use 
in one of the districts of Colorado. 

Quartz and also telluride mining is the same as any other 
form of vein mining. Fig. 49 illustrates a typical under- 
ground scene. Precautions are taken at the present time 
to prevent accidents of all types characteristic of this form 
of labor. The laws require the mine to be timbered so as to 
prevent caving in; several ways of egress are also constructed ; 
the drip water is drained and also by properly placed fans 
the air is kept in constant circulation. The ore is blasted 



THE EXTRACTION OF GOLD 



173 



from place and then carried to the surface. It is then dressed 
and concentrated and sent to the smelters or refineries. 




174 



GOLD 



Recovery of Gold from its Ores. — The methods of recovery 
of gold from its ores may be classed as follows: 



f t 


IP 

I y.'-i-i^g - 
-■'•* 

■ 


1 ' "llWjL" 






si * v > - vj^;? 



RECOVERY OF GOLD FROM ITS ORES 175 

1. Extraction by simply washing. 

2. Extraction in the dry way. 

3. Extraction in the wet way. 

4. Extraction by electrolysis. 

5. Extraction by wet and dry methods. 

Simple Washing. — Extraction by simply washing is 
effected by dressing gold-bearing sands, gravels, or ores. 

Dry Method. — Extraction in the dry way consists of 
converting the gold into gold-lead, or gold-lead-silver alloy 
and cupelling it. This method is used in extracting gold, 
when present in small but paying quantities in other ores, 
such as iron-lead and gold-bearing furnace products from 
other metallurgical reductions. 

Wet. Methods. — Under this heading there are three 
distinct processes: (1) Amalgamation process. (2) Chlori- 
nation process. (3) Cyanide process. 

Amalgamation Process. — The gold ore is treated with 
mercury and an amalgam of gold and mercury is formed. 
The amalgam usually contains silver, but is free from con- 
tamination of base metals. The mercury is boiled off, leaving 
a gold-silver alloy. A special process is necessary to free the 
gold from silver. 

Chlorination Process (Plattner or Percy Process). — This 
process consists of treating gold ores with watery solutions 
of chlorine. It is used to treat ores in which mercury has 
failed to recover all the gold present. The gold is dissolved 
as the chloride and is then precipitated from solution by the 
addition of ferrous sulphate : 

2AuCl 3 + 6FeS0 4 = 2Au + Fe 2 Cl 6 + 2Fe 2 (S04) 3 . 

In the Plattner process the following operations have to be 
considered : 

1. Clacination of the ore. 

2. Chlorinating the gold and leaching the auric chloride 
from the ore. 

3. Extraction of the gold from the solution of its chloride. 
If the gold ore contains silver, the silver chloride, being 

insoluble in chlorine, remains in the residues. In this case, 



176 GOLD 

after the gold has been removed, the residues are treated 
with hyposulphides to recover the silver. 

Cyanide Process. — Potassium cyanide in the presence of 
air possesses the property of dissolving gold according to the 
following reaction: 

8KCN+ 2Au + 20 2 + 4H 2 = 2KAu(CN) 4 + 6KOH + H2O2. 

From this solution gold may be recovered either by heating 
with zinc shavings: 

2KAu(CN) 4 + 2Zn = 2KZn(CN) 4 + 2Au 

or by electrolysis, using a cyanide bath. 

Reduction of Tellurides. — The process made use of in the 
reduction of tellurides consists of dressing and roasting the 
ore and submitting the mass to an amalgamation and cyanide 
recovery process. A description of this process will give a 
knowledge of the actual working of a gold ore. The ore is 
passed through a ball mill and crushed; it is then conveyed 
to mixing bins so as to obtain a uniform product. Belt 
conveys are then used to transfer the ore again to the ball 
mills and it is further ground, until it will pass through a 
screen one-eighth inch square. The ore is next sent to the 
roasters and the tellurium burned out first and then the 
sulphur, leaving about 0.07 per cent, of sulphur still in 
the. ore. The temperature of the roasting furnace ranges 
from 700° to 1300° F. After cooling the mass the ore is sent 
to the cyanide tanks and thoroughly mixed. The mass is 
again ground until it passes through a screen 5^ of an inch 
square. This product is then allowed to flow over blanket 
tables, upon which the -coarse particles of gold produced in 
the roasting process is recovered and subsequently reduced 
to amalgam form by pan amalgamation. The cyanide solu- 
tion is obtained from the sands and then reduced by zinc 
shavings. The gold-zinc product is placed in suitable vessels 
and the zinc dissolved and washed away. The amalgam is 
heated and the mercury driven off and the gold recovered. 

Flectro lytic Process. — This process is used for the most 
part in the treatment of gold-copper and gold-silver alloys 
and also as a "parting process." 



RECOVERY OF GOLD FROM ITS ORES 177 

Refining Gold. — Gold as it is obtained from the processes 
mentioned contains impurities. The greater part of silver 
produced contains gold as also does the greater part of the 
gold contain silver. These silver-gold and gold-silver alloys 
may also contain such metals as lead, bismuth, tin, antimony 
and arsenic, which must be removed as far as possible before 
parting by means of cupellation or refining. The process of 
parting has for its object the removal of the last traces of 
foreign elements in addition to separating silver from gold. 
Parting may be accomplished either in the dry or wet way 
or electrolytically. The dry way depends upon the conversion 
of the silver into sulphide or chloride, while gold is not acted 
upon by either chlorine or sulphur at high temperatures. 
Briefly described, the following methods are made use of in 
the dry way; 

1. The gold-silver alloy is melted with antimony sulphide, 
the silver combines with the sulphur and an alloy of antimony 
and gold results. By heating the alloy, antimony is volatil- 
ized, leaving the gold. 

2. Parting by means of sulphur and litharge. 

3. Parting by sulphur alone. 

4. Parting by means of pyrites. 

5. Parting by means of salt or cementation. 

6. Parting by chlorine gas. 

Most of these processes are obsolete; however, the last one 
is used at the present time to some extent. 

The alloy is fused in a glazed clay crucible and a covering 
of borax is used, chlorine gas is forced through the molten 
alloy and silver chloride separates from the gold. 

Wet Method of Pakting. — The wet method of parting 
is generally known as the inquartation process, because the 
gold-silver alloy is so prepared that it contains three parts 
of silver to one part of gold, making up a four-part alloy; 
from this we have the derivation of the name quartation, 
from quarter, meaning four. 

If the gold contains tin, antimony or arsenic, it should be 
refined by fusion before this process is used. Palladium, 
copper and lead may be present in the alloy without inter- 
12 



178 GOLD 

fering with this process. The alloy is prepared by adding 
a sufficient quantity of silver to approximately produce a 
l-to-3 alloy of gold and silver. The mass is granulated by 
pouring the fused alloy into water contained in a wooden 
vessel; a second granulation is desirable, as it produces a 
more homogeneous alloy. The next step is to treat the 
alloy with either nitric acid (sp. gr., 1.4), or sulphuric acid 
(sp. gr., 1.84). 

Nitric Acid Method. — The granulated alloy is placed in a 
porcelain or glazed earthenware pot and treated with about 
90 per cent, by weight of nitric acid (sp. gr., 1.4). Heat is 
applied and the granulations are stirred every twenty min- 
utes to prevent them from clotting together. After boiling 
for twelve hours and settling for twelve, the silver nitrate 
solution is diluted with water and drawn off. The residue is 
again treated with nitric acid as before for twelve hours and 
allowed to settle for the same period of time. The gold is 
filtered off and washed with boiling water and then boiled 
with sulphuric acid three times. The gold from this process 
may be obtained 999.5 fine. 

Sulphuric Acid Process. — This process is more extensively 
used than the nitric acid process. The following operations 
are embraced in this procedure : 

1. The preparation of an alloy suitable for parting and its 
granulation. 

2. The solution of the silver of the alloy by means of sul- 
phuric acid. 

3. Obtaining the gold from the auriferous residue. 

Lead, bismuth, tin, antimony, arsenic and tellurium 
seriously interfere with the malleability of gold and should be 
removed before the gold-silver alloy is prepared. From 
argentiferous gold these metals may be removed by fusing 
with potassium nitrate. Copper during this process forms 
an insoluble anhydrous copper sulphate which clings to the 
granulated metal and prevents the action of the acid. When 
copper is present in an appreciable amount the proportions 
of gold to silver should not exceed about 10 per cent. The 
alloy is prepared in other cases containing two parts of gold 



PRECIPITATION OF GOLD FROM SOLUTION 179 

to four of silver and the copper should not exceed 6 per cent. 
The granulated alloy is treated with sulphuric acid (specific 
gravity, 1.84), in three successive stages; it is then thoroughly 
washed, dried, pressed and finally melted. Its fineness is 
from 990 to 994 parts per thousand. To prepare gold of a 
higher standard than that produced from these processes, 
the following methods are made use of: 

The purest gold, completely free from silver is obtained by 
Roessler's method. The gold from the sulphuric acid parting 
is treated with aqua regia in a porcelain vessel. It is then 
precipitated by means of ferrous sulphate. The gold thus 
obtained is from 999.4 to 999.9 parts per thousand fine. By 
passing chlorine gas through molten gold a product 997 
fine can be obtained. 

Treatment of Gold Scraps in the Dry Way. — The following 
agents may be used to remove impurities from gold scraps 
in the dry way, and brittleness in a great measure may be 
overcome; it stands to reason that if the gold is desired in a 
high degree of purity, the chlorine process or aqua regia 
methods should be used. 

Potassium nitrate oxidizes certain base metals; however, 
this reagent attacks graphite crucibles, and borax which is 
used as a flux will attack fire-clay crucibles. Lead is hard to 
remove by potassium nitrate alone; however, when used in 
conjunction with ammonium chloride most of the lead will 
be oxidized and taken up by the borax. Sand may be used 
when iron is present, while potassium carbonate removes 
tin. The following is a brief outline of a method used to 
overcome brittleness: Fuse the gold, using borax as a flux 
then add ammonium chloride to remove lead and tin. 
Remove the slag and place a small quantity of mercuric 
chloride upon the surface of the molten metal ; this will 
volatilize zinc, copper, antimony and bismuth as chlorides. 
The metal is then covered with powdered charcoal, stirred 
and poured. 

Agents Used to Precipitate Gold from Solution. — Sulphurous 
acid, H 2 S0 3 , precipitates gold generally in the form of a scaly 
metallic powder; hence it does not afford masses sufficiently 



180 GOLD 

coherent or sponge-like for use as a filling material for the 
dentist. The reaction which takes place is thus explained: 

2AuCl 3 + 3H 2 + 3H2SO3 = 6HC1 + 3H2SO4 + 2Au. 

Ferrous sulphate, FeS0 4 , precipitates gold in the form of a 
light brown powder. About four times the weight of gold 
is the quantity of ferrous sulphate required to completely 
precipitate all of the gold from solution. After the finely 
divided gold has entirely subsided, it should be boiled several 
times with dilute hydrochloric acid to entirely remove all 
traces of iron. If there is a possibility of platinum being 
present, it should be precipitated first, as ferrous sulphate 
also throws this metal out of solution. The reaction of 
ferrous sulphate on gold chloride is represented by the 
following : 

A11CI3 + 3FeS0 4 = Au + FeCl 3 + Fe 2 (S0 4 ) 3 . 

Oxalic Acid, H 2 C 2 4 . — This organic acid is the best reagent 
for the precipitation of gold; however, it is somewhat slower 
in its action than the other precipitants. The gold is thrown 
down by oxalic acid in various forms, from sponge-like masses 
to the different crystalline or powdery forms. Heat is neces- 
sary and also causes the more rapid precipitation. The 
reaction is shown in the following equation: 

2AuCl 3 + 3H2C2O4 = 6HC1 + 6CO2 + 2Au. 

Gum arabic may also be used and it precipitates gold in the 
shredded form. 

Sugar, hydrogen peroxide, and certain metals among which 
may be mentioned lead, silver, mercury, tin, copper, platinum 
and zinc also precipitates gold from its solutions. The 
reaction with hydrogen peroxide is as follows: 

2AuCl 3 + 3H2O2 = 6HC1 + 30 2 + 2Au. 

Properties. — Gold possesses a beautiful yellow color, and a 
brilliant metallic luster which is unacted upon by air or 
hydrogen sulphide. It is of about the same hardness as lead. 

Gold is one of the most malleable of metals and has been 
beaten into leaves about -gtrtTft °f an mcn m thickness; 



PROPERTIES 181 

one grain of gold covering 75 square inches. Gold is gener- 
ally considered the most malleable of metals, and as has been 
elsewhere stated in this text, these figures must not be taken 
too seriously, as our methods have failed before the limits of 
malleability have been reached. In comparison with the 
above figures 1 grain of silver lias been beaten out to cover 
98 square inches ; although the silver is of less specific gravity, 
and 1 grain would necessarily mean a larger volume of this 
metal, but per weight silver appears more malleable than 
gold. To appreciate how thin a piece of metal FeiVsT °f an 
inch would be, it will take 1200 leaves of gold of this thickness 
to equal the thickness of a piece of ordinary writing paper. 

Gold is exceedingly ductile, but does not possess a very 
considerable degree of tenacity. A grain of gold, however, if 
covered with a more tenacious metal, such as silver, may be 
drawn into a wire 500 feet in length, having a diameter of 
soVo of an inch. 

The specific gravity of gold varies according to conditions. 
In the finely divided state, as it is obtained by precipitating 
with oxalic acid, it is 19.35. Cast gold is somewhat higher 
and when hammered or pressed in a rolling-mill, it may be 
raised to from 19.37 to 19.5. Annealing restores its original 
density. Gold as a conductor of electricity as compared with 
silver is 66.7; silver being 100. As a conductor of heat 532, 
silver being 1000. Its coefficiency of linear expansion between 
0° and 100° is 0.00001466. The boiling point of gold according 
to Greenwood is given as 2200° C.; however, gold containing 
other metals such as zinc, silver, copper, etc., may be volatil- 
ized at a temperature near the fusing point, or about 1120° C. 
Makins has succeeded in volatilizing it by passing a powerful 
charge of electricity through a highly attenuated gold wire 
or leaf. 

Gold Leaf and Foil. — Gold foils may be obtained in various 
colors, depending upon the alloy of gold used. The color of 
the gold is modified by the admixture of silver, producing 
light golds, and by the alloying with copper, red or dark 
shades may be produced. The following colors may be 
produced: red, pale red, extra deep red, deep red, orange, 



182 GOLD 

lemon, deep pale, pale, pale-pale, deep party, party and fine 
gold. The deeper colors are alloyed with from 12 to 16 grains 
of copper per ounce; and the middle colors, 12 to 20 grains 
of silver and 6 to 8 grains of copper to the ounce; the paler 
golds contain from 2 to 20 dwt. of silver to the ounce. 

When silver and copper are used together, it is found that 
the gold becomes brittle and cannot be reduced to the same 
degree as when these metals are used separately. 

For filling teeth nearly pure gold in the form of foil is used. 
It is generally prepared by beating, but some of the heavier 
numbers are produced by rolling. Foil gold is put upon the 
market in books containing 60 grains, the number of the foil 
represents the number of grains to the sheet; a book of No. 
2 foil contains 30 sheets, each weighing 2 grains, consequently, 
a book of No. 4 foil contains 15 sheets of 4 grains each; No. 60 
foil, each sheet weighs 60 grains and only one sheet to the book. 

There are two varieties of foils, cohesive and non-cohesive. 
Cohesive foil (hard gold). Gold in a high degree of purity 
is all cohesive, i. e., welds in the cold. This form of gold is 
called hard gold because upon working it, it looses its plia- 
bility and must be annealed in order to have its original 
softness restored. Non-cohesive (soft gold). It is the 
common belief that the property of non-cohesiveness is 
imparted to gold by some treatment of the surface or to 
the mechanical management during lamination, and not to 
alloying. Certain gases when passed over the surface of gold 
cause it to lose its cohesiveness. 

Corrugated Gold. — Corrugated gold is prepared by placing 
sheets of metal between leaves of unsized paper and tightly 
packing in an iron box, it is then exposed to a temperature 
sufficient to carbonize the paper. When cool the gold is 
found to be non-cohesive, exceedingly soft and presents a 
peculiar corrugated condition of its surface. Annealing does 
not render it cohesive. 

The process of beating gold is conducted in the following 
manner: The metal is first alloyed according to the color 
desired, and in order to improve its malleability it is melted 
at a higher temperature than is necessary for mere fusion. 



PROPERTIES 183 

It is then cast into an ingot and rolled into a ribbon of one- 
half inch in width and ten feet in length to the ounce. After 
this it is annealed and cut into pieces of about six and one- 
half grains each and placed between the leaves of a "cutch," 
which is about half an inch thick and three and one-half 
inches square, containing about one hundred and eighty 
leaves of tough paper manufactured in France. Fine vellum 
was formerly used for this purpose, and it is yet often inter- 
leaved in the proportion of about one vellum to six of paper. 
The hammer employed by gold-beaters weighs about 
seventeen pounds, and rebounds, by the elasticity of the 
skin, to such an extent that each stroke involves but little 
labor. It requires about twenty minutes' beating to spread 
the gold to the size of the cutch, and if it is intended for 
filling teeth it is carried no further than the cutch stage. If, 
however, it is to be still further attenuated, each leaf is 
taken from the cutch and cut into four pieces, when it is put 
between the skins of a "shoder," four and one-half inches 
square and three-quarters of an inch thick, containing 
about 720 skins. The shoder requires about two hours' 
beating with a nine-pound hammer. A^ the gold will spread 
unequally, the shoder is beaten upon after the large leaves 
have reached the edges, the effect of which is that the margins 
of large leaves come out of the edges in a state of dust. This 
allows time for the smaller leaves to reach the full size of the 
shoder, by which a general evenness in the size of the leaves 
is obtained. Each leaf is again cut into four pieces and 
placed between the leaves of a "mold" — an appliance 
composed of about nine hundred and fifty of the finest gold- 
beater's skins. Its dimensions are five inches square by three- 
fourths of an inch thick. The management of the gold in the 
"molds" is the last and most difficult stage in the process of 
gold-beating, and the fineness of the skin and judgment of the 
workman will greatly influence the final result. 

The process of lamination may be thus described : During 
the first hour the blows of the hammer are directed principally 
upon the center of the mold, by which means the edges of 
the leaves are made to crack, but they soon coalesce and 



184 GOLD 

unite, so that after beating no trace of the rupture is left. 
After having been beaten for an hour in a mold until the 
leaves have attained a thickness of T5~oV "oo" P ar t of an inch 
in thickness, green rays of light begin to be transmitted, if 
the gold is pure; but if largely alloyed with silver, rays of a 
pale violet hue pass through the gold. 

The membrane called "gold-beater's skin," used in the 
make-up of the shoder and mold, is the outer coat of the 
cecum or blind gut of the ox. It is immersed in a potash 
solution and scraped with a blunt knife to free it from fat. 
It is then stretched on a frame, two membranes are glued 
together, treated with camphor in isinglass and subsequently 
coated with albumen, and cut into squares of five or five and 
one-half inches, and is ready for use. It is stated that the 
ceca of 380 oxen are required to yield enough of the membrane 
to make up one mold of 950 pieces, only two and one-half 
skins being obtained from each animal. Dryness is a matter 
of great importance and, as the leaves are liable to absorb 
moisture from the atmosphere, they require hot pressing 
every time they are used, and if this precaution is neglected 
the leaf will be pierced with innumerable holes or reduced 
to a pulverulent state. 

Solubilities. — The ordinary acids are without action upon 
gold, selenic acid, H 2 Se04, is said to dissolve it and the other 
noble metals. Chlorine, bromine, and iodine dissolve gold 
with the formation of the corresponding salts. Aqua regia 
is the best solvent for gold and its action is dependent upon 
the liberation of chlorine from the hydrochloric acid by the 
oxidizing power of nitric acid. The chlorine attacks the gold 
with the formation of the trichloride; writing this reaction 
in two stages, we have the following: 

3HC1 + HN0 3 = Cl 2 4- NOC1 + H2O. 

Chlorine is given off and also nitrosyl chloride (NOC1). 

2Atf + 3C1 2 = 2A11CI3. 

The complete reaction may be represented as follows: 

2Au + 9HC1 + 3HN0 3 = 2AuCl 3 + 3NOC1 + 6H2O. 



ALLOYS 185 

Potassium cyanide in the presence of air dissolves gold, 
with the formation of potassium auric cyanide. In metal- 
lurgical operations the cyanide solution used is of about 
0.25 per cent, strength. 

Alloys. — Gold readily amalgamates with mercury in all 
proportions and the amalgam is soluble in mercury. Amal- 
gam containing 90 per cent, of mercury is fluid, with 87.5 
per cent, it is pasty, and with 87 per cent, it forms yellowish- 
white crystals. Solutions of the amalgam in mercury, when 
pressed through chamois leather, leaves a residue containing 
66 per cent, of gold and the mercury which passes through 
the leather bears a little gold, the amount depending upon the 
temperature. 

Several compounds are said to be formed corresponding 
to the formulas: 

AuHg4, AuHg3, Au2Hg3 and Au4Hg. 

The presence of lead, bismuth, cadmium, antimony, arsenic 
and tin, render gold brittle even when present in small 
quantities; 20 ] 00 part of lead, bismuth or tin produces 
brittleness in gold. Zinc also renders gold brittle but in the 
presence of copper and silver does not materially affect the 
malleability. Osmium and iridium do not alloy with gold 
but remain as grains in the molten mass. 

Silver and gold alloy in all proportions and the color of the 
gold is lightened by the addition of silver. Molten gold- 
silver alloys containing less than 20 per cent, of gold deposit; 
when slowly cooled an alloy containing one part of gold and 
five parts of silver and the mother liquid contains but little 
gold. Fenchel states that the fusing point of gold is hardly 
lowered by the addition of silver even to the extent of 50 
per cent. ; an alloy of sixty parts silver and forty parts gold 
requires more than 1050° C. to melt. Prothero calls attention 
to this same fact and states that the difference in the fusing 
point of a 50 per cent, silver alloy and that of pure gold 
could not be registered with a pyrometer. However, both of 
these authorities disagree as to the usefulness of silver in 



186 GOLD 

gold alloys. Copper and gold form a durable alloy, but in 
order to obtain a uniform product the alloy should be heated 
for some time. The malleability of the gold is not, however, 
much effected by admixtures with copper. Tin when alloyed 
to gold decreases the melting point; an alloy containing 
about 37 per cent, tin and 63 per cent, gold fuses at 418° C. 
This alloy is as brittle as glass but withstands the action of 
acids. Antimony with gold produces brittle alloys which 
are very hard and low fusing. Gold and iridium form very 
hard alloys, and the presence of iridium in gold bullion has 
caused a great amount of trouble, as such gold is extremely 
hard and interferes with the operations made use of in the 
processes of coinage. Iron and gold alloy and the alloy 
resembles iron in color, when the percentage of gold does not 
exceed 80 per cent. These alloys are said to be brittle and 
very hard to work. They have no useful application. Care 
should be taken not to contaminate gold with iron, as the 
working properties will be interfered with. It is rather easy 
to contaminate gold with iron in the dental laboratory and 
if the precaution be taken to use a magnet upon the gold 
scraps this difficulty will be overcome. In teasing solder it 
is the best practice to use a slate instrument rather than an 
iron instrument for the same reason. 

Platinum and gold alloy, producing an alloy which adds 
somewhat to the elasticity of the gold. An excess of platinum 
renders the alloy infusible in the ordinary blast furnaces. 

This alloy is used as a clasp metal in dentistry. Prothero 
claims that a 10 per cent, copper-gold alloy possesses the same 
hardness as a 25 per cent, platinum-gold alloy. 

Platinum and gold in the form of foil is also used under the 
name platinized gold*, for filling cavities, where gold has 
proved too soft. Platinized gold may be prepared by electro- 
depositing a gold surface upon platinum. 

Palladium and gold readily alloy and the hardness of gold 
is increased. There is a difference of opinion whether 
palladium renders gold brittle or not; Makins claims that 
the least trace of palladium renders gold brittle; however, 
later experiments seem to show that in reasonable quantities 



ALLOYS 187 

palladium does not affect the malleability and ductility of 
gold to any appreciable extent. 

Gold and zinc combine, forming very brittle alloys, and 
the fusing point of the gold is considerably reduced. Zinc 
is sometimes added to gold-copper alloys because of the 
reducing powders of zinc. The zinc is supposed to take up 
the oxygen and thus prevent loss of copper during the fusing 
process. 

Certain alloys of gold are used in dentistry for the construc- 
tion of metallic bases, and also as a solder. 

Gold alloys used in dentistry should be considered as to 
the character of the metals made use of. 

The requirements that such an alloy should possess are 
generally classed under the following headings: 

1. The color of the alloy should not be objectionable. 

2. It should not be acted upon by the fluids of the mouth. 
These requirements are looked to, no matter to what 

purpose the alloy is put. Little need be said in regard to the 
first requirement, for the color of any of the metals may be 
said to be objectionable at the best. 

A metallic body in the mouth may be acted upon by direct 
chemical processes ; hydrogen sulphide causes a discoloration 
in some alloys; fruit acids also may attack some metallic 
substances. Metals may also be attacked by reason of a 
difference in their electropotential, that is depending upon 
their position in the electromotive series; a voltaic couple 
may be produced, one of the metals being electropositive 
to the other and the saliva having salts in solution, there is 
then present all the elements of a so-called voltaic cell. 
Dr. C. J. Grieves has written a very interesting article upon 
the "Behavior of Certain Metals in the Mouth." Quoting 
from this article: "An alloy containing approximately gold 
18, platinum 2, the remaining 2 parts being made up of 
equal parts silver, copper and zinc, after short wear under 
like conditions presents corrosion almost as pronounced as 
German silver." "The study of a large number of 18-carat 
gold solder surfaces known to have been smooth when placed 
in the mouth, develops the interesting fact that whenever 



188 GOLD 

a food-retention center was created, corrosion exists to a 
marked degree." 

Considering the first alloy mentioned, gold, platinum, silver 
and copper are classed as negative metals, while zinc is 
strongly electropositive; the greatest potential difference 
exists between gold and zinc, and from this point of view the 
alloy would be more resistant to the action of the saliva, 
if zinc would have been eliminated. The same may be said 
of the 18-carat solders containing zinc. Working upon this 
principle, an alloy to possess the greatest resistance to the 
fluids of the mouth should contain only those metals from 
hydrogen to gold (see electromotive series). 

Gold is Alloyed for Dental Purposes. — 1. To increase its 
hardness. 

2. To lower its fusing point, as in the construction of 
solders. 

3. To increase its elasticity, as in the construction of 
clasp metal. 

Depending upon the quantity of gold present in an alloy, 
pure gold is taken as a standard and called 24-carat; the 
degree of fineness is expressed on a basis of twenty-four 
parts. 

The carat is the term used to express the purity of gold and 
represents one-twenty-fourth parts. 

Plate gold is generally expressed in caratage; that is, 
22-carat plate gold contains twenty-two parts of pure gold 
and two parts of the metals. 

Solder is expressed in caratage of the gold for which it is 
intended to be used upon as a solder. For example, 18-carat 
gold solder is not 18 carats fine, but is supposed to be used as 
a solder for 18-carat, or better, plate gold. Eighteen-carat 
solder generally is about 16 carats fine. 

The hardness of gold is increased in order for the gold to 
withstand the form of attrition to which it is subjected during 
the process of mastication. 

Copper is a very serviceable metal for this purpose; 
however, it reduces the fusing point of gold. The alloy is of a 
dark red color, and copper is also liable to oxidation on 



TO LOWER THE FUSING POINT OF GOLD 189 

overheating. There is very little electropotential difference 
between copper and gold. These metals should be alloyed 
and kept in the molten condition for some time, so as to 
obtain a homogeneous mixture ; the surface of the molten 
metals also should be protected to prevent loss by oxidation 
while alloying. The United States gold coin contains copper 
to harden the gold; it is made up of gold ninety parts and 
copper ten, or about 21.6 carats fine. 

Silver hardens gold and tends to lighten its color; in larger 
proportions an alloy results having a brassy appearance. 
The fusing point of the alloy is scarcely altered. In alloying, 
the metals must be kept in the state of fusion for some time, 
in order to obtain a uniform mixture. 

To Lower the Fusing Point of Gold.— Zinc and copper have 
been the principal metals used in dental gold, which reduced 
the fusing point to the extent that was necessary for soldering 
purposes. Dr. Dorrance prepares an alloy consisting of: 

Pure silver 1 pennyweight 

Pure zinc 2 pennyweights 

Pure copper 3 pennyweights 

To prepare a solder for a given carat gold, a piece of the 
plate gold is alloyed with a given quantity of this alloy; for 
example, if 22-carat plate is to be soldered, then 22 grains 
of the plate is alloyed with 2 grains of the Dorrance alloy. 

Gold plate suitable for dental purposes may be prepared 
according to the following formulas, from Richardson's 
Mechanical Dentistry: 

Gold Plate 18 Carats Fine. 

No. 1. No. 2. 

Pure gold . 18 pennyweights Gold coin . 20 pennyweights 

Pure copper 4 pennyweights Pure copper 2 pennyweights 

Pure silver . 2 pennyweights Pure silver . 2 pennyweights 

Gold Plate 19 Carats Fine. 

No. 3. No. 4. 

Pure gold . 19 pennyweights Gold coin . 20 pennyweights 

Pure copper 3 pennyweights Pure copper 25 grains 

Pure silver . 2 pennyweights Pure silver . 40 + grains 



190 GOLD 

Gold Plate 20 Carats Fine. 

No. 5. No. 6. 

Pure gold . 20 pennyweights Pure gold . 20 pennyweights 

Pure copper 2 pennyweights Pure copper 18 grains 

Pure silver . 2 pennyweights Pure silver . 20 + grains 

Gold Plate 21 Carats Fine 

No. 7. No. 8. 

Pure gold . 21 pennyweights Gold coin . 20 pennyweights 

Pure copper 2 pennyweights Pure silver . 3 + grains 
Pure silver . 1 pennyweight 

No. 9. 

Gold coin 22 pennyweights 

Pure copper 6 grains 

Pure platinum 7y grains 

Gold Plate 22 Carats Fine. 

No. 10. 

Pure gold 22 pennyweights 

Fine copper 1 pennyweight 

Pure silver 18 grains 

Pure platinum 6 grains 

Gold Plate 18 Carats Fine. 

No. 11. 

United States gold coin ($60) ...... 64J pennyweights 

Pure silver 13 pennyweights 

On account of its greater strength and the power of resist- 
ing chemical action of the fluids of the mouth, many dentists 
prefer to use gold plate of 20 or 21 carats fine, in which the 
resulting constituents are copper and platinum, the following 
formula being an example: 

Gold coin 20 pennyweights 

Pure platinum 10 grains 

The following formulas will produce alloys of 20 carats 
fineness, suitable for clasps, backings, etc., wherever elasticity 
and additional strength are required: 

Formula No. 1. Formula No. 2. 

Pure gold . 20 pennyweights Coin gold . 20 pennyweights 

Pure copper 2 pennyweights Pure copper 8 grains 

Pure silver . 1 pennyweight Pure silver . 10 grains 

Pure platinum 1 pennyweight Pure platinum 10 grains 



ALLOYS OF GOLD IN DENTISTRY 191 

Alloys of Gold Employed in Dentistry as Solders. — These 
are a class of alloys formed of the metal to be united, the 
fusing point of which is reduced by the addition of silver or 
copper. 

14 Carats Fine. 16 Carats Fine. 

American gold coin . $10.00 Pure gold . . 11 dwts. 

Pure silver .... 4 dwts. Pure silver . . 3 dwts., 6 grs. 

Pure copper ... 2 dwts. Pure copper . 2 dwts., 6 grs. 

20 Carats Fine, tor Crown and 
18 Carats Fine. Bridge-work. 

Gold coin .... 30 parts American gold coin 

Pure silver .... 4 parts (21.6 carats fine) 

Pure copper .... 1 part $10 piece . . . 258 grs. 

Brass 1 part Spelter solder . . 20.64 grs. 

20 Carats Fine, for Crown and 
20 Carats Fine. Bridge-work. 

Pure gold . . 5 pennyweights Zinc ... 1 \ grains 

Pure copper . 6 grains Pure gold . 20 grains 

Pure sih er . 12 grains Silver solder 3 grains 

Spelter s )lder 6 grains 

Dr. C. M. Richmond's solder for bridge- work: 

Gold coin 5 pennyweights 

Fine brass wire 1 pennyweight 

Dr. Low's formula for solder in crown and bridge-work: 

19 Carats Fine. 

Coin gold 1 pennyweight 

Copper 2 grains 

Silver . 4 grains 

Spelter solder, composed of equal parts of copper and zinc, 
is sometimes employed as a constituent in the preparation 
of gold solders for the purpose of reducing the fusing point. 
Thus some dentists use an alloy composed of: 

18-carat gold 6 pennyweights 

Granulated spelter solder . . . . . . .6 grains 

An alloy of this composition is exceedingly brittle, and 
hence difficult to roll into plate without breaking into many 
pieces. Its color is good, but the surface of such solders, 
after flowing, is apt to be pitted with small holes, and has 



192 GOLD 

not the solid and uniform appearance that is desirable. This 
may be due to the oxidation and escape of some of the zinc. 
The following gold alloys for dental purposes have been 
recommended by Dr. Prothero: 







Plati- 


Pallad- 








Fusing 




Gold. 


num. 


ium. 


Silver. 


Copper. 


Carat. 


point. 


Gold plate No. 1 


. 88.0 


7.5 


2.5 


2.0 




21.1 


2075° F 


Gold plate No. 2 


. 84.5 


8.5 


2.0 


0.5 


4.5 


20.18 


1975° F 


Casting gold "B" 


. 80.0 


9.5 


2.5 


1.0 


7.0 


19.2 


1900° F 


Casting gold "C" 


. 80.5 


6.5 


2.0 


2.0 


9.0 


17.7 


1800° F 



Methods of Reducing Gold to a Lower or Higher Standard of 
Fineness, and of Determining the Carat of any Given Alloy. — 
In mintage the proportion of gold in an alloy is expressed 
in one-thousandths, but in the jewelry trade the term carat 
is used to designate the proportion, and it is equal to one- 
twenty-fourth. For instance, 6-carat gold means that of 
twenty-four parts of a given alloy, six parts are gold. The 
gold alloys used in the laboratory are generally made from 
pure gold or gold coin, the standards of which are definitely 
fixed. A few simple rules are here given, 1 by which the 
operator may readily determine the quantity of alloy neces- 
sary to reduce either coin or pure gold to any desired standard. 
To ascertain the carat of any given alloy, multiply 24 by 
the weight of gold in the alloyed mass and divide the prod- 
uct by the weight of the mass. The quotient is the carat 
sought. For example, take the following: 

Pure gold 18 parts 

Copper 4 parts 

Silver 2 parts 

24 parts 

The result may be thus expressed: 

24 X 18 -f- 24 = 18 carats. 

To reduce gold to a required carat, multiply the weight 
of gold used by 24 and divide the product by the required 
carat. The quotient is the weight of the mass when reduced, 

1 Richardson's Mechanical Dentistry. 



ALLOYS OF GOLD IN DENTISTRY 



193 



from which subtract the weight of the gold used, and the 
remainder is the weight of the alloy to be added. 

To raise gold from a lower to a higher carat, multiply the 
weight of the alloyed gold used by the number representing 
the proportion of alloy in the given carat; divide the product 
by the figures representing the quantity of alloy in the 
required carat. The quotient is the weight of the mass when 
reduced to the required carat by adding fine gold. Thus, to 
raise 1 pennyweight of 16-carat gold to 18 carats, the numbers 
representing the proportions of alloys are obtained by sub- 
tracting 18 and 16 from 24. The statement is: 

6:8:.'l:'li; 

from which it will be seen that to raise 1 pennyweight of 
16-carat gold to 18 carats, one-third of a pennyweight of 
pure gold must be added to it. 

Again, if instead of using pure gold we desire to raise the 
fineness of 1 pennyweight of 16-carat gold to that of 18, by 
the addition of, say, 22-carat gold, the numbers representing 
the proportions of the alloy would be found by subtracting, 
in the example given, 16 and 18 from 22, the result being: 

4:6::1:1*. 



Hence, each pennyweight of 16-carat gold would require a 
half-pennyweight of 22-carat gold to raise it to 18 carats. 
The former is the system employed at the United States 
Mint and by metallurgists and chemists, while the latter is 
the usual method of expressing the grade of alloys of gold 
among dentists and jewelers. The following table will show 
the relation of one to the other: 



Pure gold . 
English coin 
American coin 
Dentists' gold 
Dentists' gold 
Jewellers' gold, best 
Jewellers' gold, good 
Jewellers' gold, low grade 
Common jewellers' solder 
13 



Carats. 


Decimals 


24.0 


1000.0 


22.0 


916.6 


21.6 


900.0 


20.0 


833.3 


19.2 


800.0 


18.0 


750.0 


15.0 


625.0 


12.0 


500.0 


8.0 


333.3 



194 GOLD 

Purple of Cassius. — Purple of Cassius is the material used 
to impart the color to a porcelain body, imitating the color 
of the soft tissues of the mouth. It is named after the dis- 
coverer, M. Cassius, who first employed this material for the 
above purpose. It may be prepared in the wet way by adding 
stannous chloride containing a little stannic chloride to the 
chloride of gold. A purple precipitate is formed, the composi- 
tion of which is not definitely known. However, it is sup- 
posed by some to be stannous stannic oxide, aurous and auric 
oxide. As prepared in this manner "Oswald" claims the 
precipitate to be colloidal gold in stannic acid. The following 
methods may be used when a quantity of this material is 
desired: Seven parts of gold are dissolved in aqua regia and 
mixed with two parts of tin, also dissolved in aqua regia. 
This solution is largely diluted with water, and a weak solu- 
tion of one part of tin in hydrochloric acid is added, drop by 
drop, until a fine purple color is produced. The purple of 
Cassius, in a state of fine division, remains for a time sus- 
pended in the water, but finally subsides as a purple powder. 
The fresh precipitate dissolves in ammonia, and exposure 
to light decomposes the purple solution, during which process 
its hue changes to blue, and it finally becomes colorless, and 
metallic gold is precipitated, the binoxide of tin being left 
in solution. 

The Dry Method. — The dry method is the one mostly 
employed now in the manufacture of this article. Professor 
Wildman is the authority for the following procedure: 
240 grains of pure silver, 24 grains of pure gold, and 17J 
grains of pure tin are placed in a crucible, with sufficient 
borax to cover the mass, and melted. In order to ensure a 
thorough mixture of the different metals the melted mass 
should be poured from a height into a vessel of cold water, 
and this process of granulation should be repeated at least 
three times, but at every melting the alloy should be well 
covered with borax to prevent loss of the tin by oxidation. 
The vessel into which the melted mass is poured should not 
be a metallic one. 

The component parts of the alloy having now been thor- 



COMPOUNDS OF GOLD 195 

oughly incorporated, the next step is to collect the granulated 
mass and separate from it any adherent particles of glass of 
borax. The metal is then put into a glass or porcelain 
evaporating dish (the Berlin porcelain is the best), and suffi- 
cient chemically pure nitric acid is added to cover the metal. 
The dish is now placed over a sand-bath, and gentle heat 
applied and continued until chemical action ceases. If at 
this point it is found that all the metallic particles are dis- 
solved, the dish may be removed from the bath. Should 
any solid particles be found in the solution, a little more 
nitric acid must be added and the operation continued until 
all are dissolved. The silver having been entirely dissolved 
by the nitric acid, the solution should be poured off, and the 
remaining oxide carefully washed until the last trace of silver 
is removed. After several washings with a large quantity of 
pure warm water, the latter should finally be tested with a 
clear solution of common salt, and if it remains clear, without 
show of milkiness, the silver is all removed. When the oxide 
is sufficiently washed the purple of Cassius should be dried 
by gently heating, after which it is ready to be incorporated 
with the silicious materials. 

Compounds of Gold. — Gold forms two series of compounds: 
aurous and auric; in the first it has a valancy of one, while 
in the second it is trivalent. The aurous compounds are 
very unstable. 

It forms two oxides: aurous, Au 2 and auric, Au 2 3 . 
Aurous oxide is very unstable and when treated with dilute 
hydrochloric acid, auric chloride is formed. When heated 
to 250° C. it decomposes with the liberation of metallic gold. 
It is a violet-colored powder. Auric oxide acts both as a 
feeble acid and as a basic oxide. It is a brown powder and 
when treated with water and heated, forms Au 2 03.3H 2 0, 
or Au(OH) 3 . At 100° C. it begins to decompose into gold and 
oxygen. As a basic oxide it forms a few unstable salts with 
certain acids in which gold replaces the hydrogen of the acid. 
As an acid oxide it combines with certain metals, forming 
aurates. With ammonia this compound forms an explosive 
substance, fulminate of gold. 



196 GOLD 

Chlorides of Gold. — Gold forms two principal chlorides: 
aurous chloride, AuCl, and auric chloride, AuCl 3 . 

Aurous Chloride. — Aurous chloride is formed when auric 
chloride is heated to 180° C. It is a white powder, insoluble 
in water, but upon boiling is Converted into auric chloride 
and free gold is liberated. 

Auric Chloride. — Auric chloride is obtained by treating 
gold with aqua regia or chlorine and evaporating to dryness. 
When the residue is dissolved in water the concentrated 
solution deposits reddish crystals of the composition AuCl 3 .- 
2H 2 0. Auric chloride forms compounds with alkali salts 
and also with hydrochloric acid, the latter may be repre- 
sented by the formula, AuCl 3 .HCl or HAuCL, known as 
chlor auric acid. This compound is deposited from a strong 
solution of gold in aqua regia in crystalline form, having 
the composition AuCl 3 HC1.3H 2 0. 

Gold does not form sulphides in the dry way but may be 
precipitated from solution of a soluble salt by hydrogen 
sulphide. 

Two sulphides have been obtained in this way, aurous, 
Au 2 S, and auro-auric, Au 2 S, Au 2 S 3 or 4(AuS). 

Fire Assay for Gold and Silver. — The following method is 
one of many that may be used in determining the quantity 
of gold present in an ore. The system of weights used are so 
constructed that the same ratio exists between the assay 
ton weight and a milligram as between an ounce and a ton. 
There are 29166 Troy ounces to a ton, and an assay ton weighs 
29.166 grains; then on comparison there are 29166 milli- 
grams to the assay ton and the ratio between 1 milligram 
and an assay ton is as 1 to 29166, which is the same as the 
Troy ounce to the ton. 

The weight of the gold bead obtained from an assay will 
then represent the number of ounces of gold to the ton of ore. 

A high-grade gold ore is one that contains five dollars or 
more of gold to the ton of ore, that would equal about 0.242 
ounce and the gold bead weigh 0.242 milligram. 

Procedure. — If the ore contains sulphur it must be desul- 
phurized by roasting. To facilitate this process, iron nails 



FIRE ASSAY FOR GOLD AND SILVER 197 

are sometimes added to the ore, to assist in taking up the 
sulphur. 

The ore is next submitted to the crucible process. A charge 
is prepared, consisting of the following: 

Ore 1 assay ton 

Sodium bicarbonate 1| " 

Potassium carbonate \ " 

Litharge \\ " 

Silica 1 

Borax glass \ " 

Charcoal £ 6 grain. 

Salt to cover. 

The charge is placed in a Battersea crucible of suitable 
size and then introduced into the furnace. The litharge is 
reduced to metallic lead, which then dissolves the gold and 
silver from the ore and the salt covering and fusible slag 
formed prevent the oxidation of the reduced metals. After 
the charge has been in the furnace for about twenty minutes, 
the crucible is removed and the lead is poured into a suitable 
mold. The lead button obtained from this process usually 
is too large for direct cupellation; to reduce the size of same 
it is submitted to a scorification process. 

The lead is hammered into the shape of a cube and then 
weighed, the average cupel can take care of a lead button 
weighing 25 grams; however, if it weighs more than this 
amount the button is placed in a scorifier and covered with 
borax. The scorifier is then placed in a muffle furnace and 
the lead oxidizes. When sufficient lead has been removed 
the molten mass is again poured into an ingot mold. The 
lead is freed from the slag and again hammered into a cubical 
form and is ready for cupellation. 

A cupel is constructed of bone ash; sometimes a little 
sugar is added so as to make the mass more porous. The 
cupel is placed in the muffle furnace and heated until all of 
the lead has been removed. This point may readily be per- 
ceived by a peculiar phenomenon which takes place in the 
molten metals. The button of silver, gold and lead appears 
to revolve with great velocity, and rainbow colors succeed 
one another over its surface. Finally a film passes over the 



198 GOLD 

bead, and then no more action is visible. This point is known 
as the "blicking point." The bone ash of the cupel possesses 
the property of absorbing lead oxide and thus keeps the 
button free from this agent. The cupel is removed from the 
furnace and the button weighed, it is then subjected to the 
parting process. The parting process is dependent upon the 
solubility of silver in a l-to-3 gold-silver alloy in nitric acid. 
The color of the button is an indication as to the quantity of 
gold present, and if there is evidence that there is not sufficient 
silver in the button, more silver may be added. 

The button is then flattened and placed in a flask, nitric 
acid, specific gravity 1.2, is added'. The flask is heated until 
all chemical action ceases; the liquid is then filtered and the 
gold collected and weighed. The difference between the- 
weight of gold and the weight of the button received from the 
cupel is the weight of silver. 

Resume. 

Symbol, Au. Crystalline form, isometric. 

Valency, I to III. Chief ore, native metal. 

Atomic weight, 197.2. Conductivity of heat, 532. 

Melting point, 1120° C. Conductivity of electricity, 
Specific heat, 0.0324. 72.55. 

Boiling point, 2200° C. Coefficient of expansion, 
Color, yellow. 0.00001466. 

Malleability, 1st. Ductility, 1st. 

Specific gravity, 9.3 to 191.5. Tenacity, 5th. 



CHAPTER XVI. 
PLATINUM. 

Symbol, Pt. Atomic weight, 195.2. 

Occurrence. — Platinum occurs in nature in but few min- 
erals. The principal source is from native platinum, which 
also carries iron, palladium, osmium, rhodium, iridium and 
copper as impurities. It also occurs as the arsenite, PtAs 2 , 
sperrylite, and as impurities in iridosmium, IrOs. The 
greater part of the world's supply is obtained by washing 
placer deposits in the Ural Mountains. The gold placers in 
Columbia, South America, is the second district of impor- 
tance in the production of platinum, although it furnishes 
only about one-twentieth of the quantity obtained from 
Russia. A valuable deposit has recently been reported in 
Spain. Platinum is found in nature as flattened grains of the 
native metal containing about 51 to 86 per cent, platinum. 
The only native compound, sperrylite, is found at Sudbury, 
Canada, as impurities in the nickel-bearing pyrrhotite and 
calcopyrite and also in the cupric sulphide occurring in 
Wyoming. 

Historical. — The first mention of platinum was by Antonio 
de Ulloa, a Spanish naval officer, in a book published in 1748. 
In his narrative he mentions the finding of platina (Spanish 
diminutive of plata, silver) in the Choco District of Columbia 
in which it is admixed with gold. Ulloa is given credit for 
the introduction of platinum in 1735. Wood a few years later, 
1741, also makes mention of this metal. 

Platinum was at first considered an objectionable metal, 
because it interfered with the working properties of gold. 
Watson, in 1750, and Scheffer, 1752, were the first to describe 
the metal. The German chemist Margraf was the first 
investigator to obtain platinum in a fairly pure condition. 



200 PLATINUM 

He obtained the metal by acting upon platinum chloride 
with potassium and sodium salts and then upon heating 
obtained spongy platinum. In 1819 platinum was discovered 
in the Ural Mountains. Wollaston next introduced a method 
of obtaining malleable platinum from the pure spongy metal, 
but the great difficulty to be overcome was to fuse it in large 
quantities. Deville and Debray, in 1858, devised a process 
by which large quantities of the metal can be melted. 

Reduction. — Wollaston s Process. — The ore is first washed 
and then treated with hydrochloric acid; this dissolves the 
base metals. The ore is next treated with aqua regia, which 
dissolves palladium, rhodium, platinum and a little iridium 
as the chlorides. The osmium in the ore partly distils over 
as osmium peroxide and partly remains undissolved as an 
alloy with the iridium, together with ruthenium, chrome iron 
ore and titanic iron. The proportions of acids are one hun- 
dred and fifty parts hydrochloric to forty parts of nitric. 
Three or four days are necessary to dissolve the ore, aided by 
gentle heat. The solution containing the platinum is neutral- 
ized with sodium carbonate and the palladium is precipitated 
as cyanide, Pd(CN) 2 , by the addition of mercuric cyanide. 
The platinum, is next precipitated by adding ammonium 
chloride with the formation of yellow crystalline ammonio- 
platinic chloride, (NH 4 ) 2 PtCl 6 . If rhodium is present, it 
must be removed at this stage. Its presence will manifest 
itself by the solution from which the platinum has been 
precipitated, changing to a rose color. This rose color solu- 
tion may also contain about 11 per cent, of the platinum. 
Rhodium may be recovered by mixing the precipitate with 
potassium acid sulphate, KHSO4, and heating to redness 
in a platinum crucible. The rhodium is converted into 
rhodium potassium sulphate, which may be removed from 
the spongy platinum by dissolving with boiling water. The 
11 per cent, of platinum in the mother liquor is treated with 
zinc strips which precipitates the platinum with the other 
metals present. A small quantity of strong hydrochloric 
is added to avoid precipitating lead or palladium, when the 
remainder of the platinum is thrown down with ammonium 



REDUCTION 201 

chloride. The ammonium chlorplatinate is thoroughly 
washed in cold water, to remove iridium, which also forms a 
double salt with ammonium chloride. The next stage in the 
operation consists in separating the metal from the 
ammonium salt by ignition, and, as it is important to the 
success of the subsequent working that the precipitate shall 
remain in a finely divided state; too high a degree of heat 
must be avoided, as otherwise cohesion of the particles will 
take place. Ignition is generally accomplished by the 
following means: The precipitate is heated in a graphite 
crucible until nothing remains but the finely divided platinum. 
This is powdered, should it be found somewhat lumpy, 
in a wooden mortar with a wooden pestle, sifted through a 
fine lawn sieve, and mixed with water to the consistency of a 
paste. This is placed in a brass mold with a slightly tapering 
cylindrical cavity about seven inches in length, provided 
with a loosely fitting steel stopper, which enters to the depth 
of a quarter of an inch. The mold is first oiled and set up 
in a vessel of water. The platinum mud is then introduced, 
and as it settles into the water, air is displaced, and the 
platinum is thus made to fill every part of the mold. The 
water is allowed to drain, and its removal may be aided by 
pressure. Ultimately, however, the mold is placed in a 
press worked by a powerful lever, by which the mass sustains 
an enormous pressure, after which the plug and the column 
of platinum are removed by gently tapping the mold. It is 
then heated in a charcoal fire, in order to thoroughly dry it 
and to burn off any adherent oil. 

The next step, which depends upon the quality of welding 
possessed by platinum, consists in heating the porous 
cylinder in a blast furnace to white heat, when it is removed, 
set upright on an anvil, and hammered on the ends, in order 
to weld the particles; after which it is coated with a mixture 
of borax and carbonate of potash, and again heated for the 
purpose of removing traces of iron, which are dissolved by the 
mixture, the latter being removed by immersion in dilute 
sulphuric acid. The bar of platinum is now ready for use, 
and may be rolled or hammered. 



202 , PLATINUM 

It may readily be surmised that so imperfect a means of 
obtaining a solid bar of metal as the latter part of the opera- 
tion just described cannot always be relied upon for the 
production of a uniform and solid specimen; and, indeed, 
platinum prepared in this way, though of great purity, is 
liable to blister upon its surface, this being probably due to 
minute bubbles of air encased in the body of the ingot 
during the forging, which during the conversion of the in- 
got into plate by means of rollers, are elongated and spread 
out in the form of blisters. 

Deville and Debray Process. — The dry metallurgical 
operations of Deville and Debray consist in heating in a 
reverberatory furnace about two hundred pounds of platinum 
ore with an equal weight of galena (lead sulphide). When 
the ore is sufficiently heated (to bright redness), portions of 
the galena are added and mixed with the ore by constant 
stirring. An equal quantity of litharge is next added, in 
order to supply oxygen to the sulphur of the lead ore, which 
passes off as sulphurous anhydride, reducing all of the lead 
which combines with the platinum. After remaining in a 
state of fusion for a short time the upper portion is ladled 
off, and will be found to consist of an alloy of lead, platinum, 
and smaller portions of palladium and silver, the latter being 
introduced from the galena, which always contains more or 
less silver. The heavier metals of the platinum group, by 
their greater density, subside to the bottom. 

Cupellation is now resorted to in order to separate the 
platinum from the lead. This consists of two distinct 
operations. The first is performed at the ordinary furnace 
temperature, and is continued until by loss of lead the fusing 
point of the remaining alloy rises to such an extent that a 
state of fusion can no longer be maintained. The second and 
final operation is performed in an apparatus which serves 
the purpose of both furnace and cupel. It is formed of 
blocks of thoroughly burned lime. In form it may be 
described as a sort of basin or concavity, with a similar piece 
for a cover. The lower part is intended for the reception of 
the metal; through the center of the upper portion or cover 



PROPERTIES 203 

pass the tubes for the oxhydrogen jet, while the lower portion 
is divided with a lip or spout for pouring the melted metal. 
The tubes which pass through the top for the transmission 
of the two gases are generally formed of copper, with platinum 
tips. The outer and lower tube carries hydrogen, while the 
inner and upper one carries a jet of oxygen into the middle 
of the flame. The tubes are furnished with stopcocks so 
that the supply may be regulated. When the object is merely 
to fuse some scraps of platinum the lime furnace is first 
put together, the hydrogen jet is lighted, oxygen is then 
turned on, and the interior of the apparatus soon becomes 
heated. The platinum is then introduced in pieces through a 
small hole at the side, and quickly fuses after entering the 
furnace. 

When used as a cupel the lime absorbs the impurities and 
the platinum is kept in a state of fusion until all the lead is 
oxidized, when the metal may be poured from the lime cupel 
into an ingot mold formed of coke or plates of lime. Some 
difficulty may be experienced at the moment of pouring, in 
consequence of the dazzling white surface of the molten 
metal. From seven to eight pounds may be melted in this 
way in from forty to sixty minutes. 

Although such metals as palladium, osmium, gold, silver, 
and lead are volatilized at the intense heat used, it has been 
found that platinum obtained by the Deville-Debray method 
is not as pure as that obtained by Wollaston's plan. 

Properties. — Platinum is a tin-white metal, softer than 
silver but is hardened by the admixture of other metals, 
especially iridium. It is surpassed in malleability by gold 
and silver, but in ductility it in all probability stands first. 
W r ollaston succeeded in drawing it out into a wire 30J00 of 
an inch in diameter, while the smallest gauge of gold wire 
that has been reported is 5--0V0 °f an mcn - Platinum is more 
tenacious than gold, and as tenacity has a direct influence 
upon ductility it is more than probable that platinum is 
more ductile than gold. Platinum possesses about the same 
coefficient of expansion as glass; this property renders it 
invaluable to dentistry and the arts. When platinum is 



204 PLATINUM 

baked in porcelain, and the mass cools, it will be found that 
platinum contracts at the same rate as the porcelain, thus 
insuring an absolutely tight joint. In the manufacture of 
incandescent globes, platinum is used where the filament 
penetrates the glass. The globe is a partial vacuum, and any 
other metal will be found to contract, upon cooling, at a 
different rate from the glass and thus forming an imperfect 
joint, leakage would result and the vacuum be destroyed. 
Because of the recent abnormal price of platinum, substitutes 
have been offered the dental profession; a substitute to be 
of value should possess the following qualities in order to 
be of service: 

1. It should possess a high fusing point. 

2. It should have about the same coefficient of expansion 
as platinum; 

3. It should be able to withstand the action of chemical 
substance. 

4. It should be easily soldered. 

5. The price should not be prohibitive. 

Platinum fuses at about 1753° C. Small quantities may 
be fused with the oxyhydrogen blow-pipe, but in large 
quantities fusion is usually accomplished by the use of a 
lime furnace and a powerful oxyhydrogen blow-pipe (Fig. 50) . 

Platinum does not combine with oxygen at any tempera- 
ture, nor does it absorb this gas, but in the cold it condenses 
oxygen upon its surface. A piece of platinum foil, when 
introduced into a mixture of oxygen and a readily inflam- 
mable gas, causes them to combine. This action is more 
rapid in the case of platinum sponge, where a larger surface 
is brought into play, and a fragment of this material intro- 
duced into a detonating mixture of oxygen and hydrogen 
at once causes it to explode. 

Platinum may be welded at white heat, and vessels made 
of platinum may be repaired in this manner. In the finely 
divided state it may be made into small vessels by pressing 
the powdered mass of platinum into suitable molds, heating 
and hammering to complete the welding of the particles. 

Platinum is a very poor conductor of electricity, and when 



PROPERTIES 



205 



a current is passed through a platinum wire of small diameter 
the resistance offered to the flow of the electric current is so 
great that the wire becomes hot and glows; advantage is 
taken of this in the construction of the small electric furnaces 
used in dentistry. The heating element consists of a platinum 
loop imbedded in the fire-clay lining. The electric switch- 
boards have a platinum electrode used as a root-canal dryer. 
Electric annealers, sterilizers and various other forms of 




Fig. 50 



electrical contrivances also make use of platinum in the same 
capacity. In the electromotive series, platinum with gold 
are the most electronegative of the metals, and metals which 
dissolve but slowly in acids are more rapidly acted upon when 
placed in contact with platinum, forming a so-called platinum 
couple. Solutions of antimony when placed in hydrochloric 
acid and a zinc platinum couple is introduced into the acid, 
the zinc is rapidly attacked and the antimony is deposited 
upon the platinum. In chemical reactions, platinum and its 



206 PLATINUM 

salts possess a peculiar property of facilitating chemical 
action without being acted upon themselves; in other words, 
it acts as a catalytic agent. In the manufacture of sul- 
phuric acid by the contact process, platinum salts cause an 
oxidation of sulphur dioxide to the trioxide by its mere 
presence, illustrating the catalytic action of platinum salts. 

Platinum black is platinum in an exceedingly fine state of 
subdivision formed when platinum is precipitated from solu- 
tion by reducing agents or metals. It is a soft, black powder, 
which is capable of absorbing enormous quantities of oxygen. 
Platinum black absorbs about eight hundred times its 
volume of oxygen, no chemical union taking place, and hence 
it acts as a very powerful oxidizing agent. 

Platinum readily combines with phosphorus, silicon and 
carbon. The carbide of platinum is formed when the metal is 
continuously heated by a smoky flame or one in which 
combustion is incomplete. 

Compounds.— There are two oxides of platinum: platinous 
oxide, PtO, and platinic, Pt0 2 . 

Platinous oxide is formed when platinous hydroxide is 
boiled. It is a black powder, easily soluble in hydrochloric 
acid. 

Platinic oxide is formed by gently heating platinic 
hydroxide. It is a black or grayish-black powder. When 
strongly heated both of these oxides are reduced to metallic 
platinum. 

Platinum forms two chlorides : platinous, PtCl 2 , and platinic, 
PtCl 4 . 

Platinic chloride is formed by treating platinum with 
aqua regia ; if this be heated to 250° platinous chloride will be 
formed. The platinum salts possess the property of com- 
bining with others, forming double salts. With ammonium 
or potassium chloride the resulting compounds are insoluble 
in water. 

Solubilities. — The best solvent for platinum is aqua regia, 
with the formation of platinic chloride. The reaction may be 
represented as follows : 

Pt + 6HC1 + 2HN0 3 = PtCl 4 + 4H 2 + 2NOCL 



ALLOYS 207 

It is not as readily acted upon by these acids as is gold. 
Platinum is not affected by water or by air at any tempera- 
ture; it is not sensibly tarnished by hydrogen sulphide, nor 
is it attacked by sulphuric, by hydrochloric or nitric acids. 

Silver alloyed up to 10 per cent, of platinum is attacked 
by nitric acid; any larger proportion of platinum will remain 
undissolved. Platinum is also attacked by fusing with caustic 
alkalies and alkali nitrates, so care should be used not to fuse 
these compounds in platinum vessels 

Alloys. — Gold and platinum alloy and the resultant alloy 
has a greater coefficient of elasticity than either metal. In 
dentistry this alloy is used for clasp metal and also for casting 
in crown and bridge-work. Fenchel quotes Bornemann, that 
the hardness steadily increases with 20 to 30 per cent, 
platinum, when it equals that of pure platinum, and then 
increases up to 50 per cent., when the hardness equals that 
of calcareous spar. It then falls again to the platinum level. 
An excess of platinum renders the alloy infusible in the 
ordinary furnace. The tenacity of gold is increased while 
the malleability is somewhat impaired. The color of the 
alloy is not so brilliant as that of gold when equal parts of 
the two metals are alloyed. Foils of so-called platinous gold 
are also used for a filling material; this so-called platinous 
gold possesses hardness, but it is more difficult to work and 
the color is objectionable to some individuals. 

Platinum solder usually contains from fifteen to twenty- 
five parts of platinum alloyed with gold. Pure gold is also 
used in soldering platinum; a minimum amount of gold is 
used and any excess should be driven off by heating, especially 
in joints to be covered by porcelain, as there is a liability of 
the excess gold volatilizing at the high temperature of the 
porcelain furnace which would result in gassing the por- 
celain. 

Silver and platinum alloy in all proportions, forming 
alloys which are harder than silver, and the color is between 
that of silver and platinum. The alloy is hardly more resist- 
ant to the action of reagents than pure silver. Hot sulphuric 
and nitric acids attack it. An alloy containing about 25 to 30 



208 PLATINUM 

per cent, of platinum is known as " dental alloy" and has been 
used in Europe for making dental bases. 

Mercury and platinum do not amalgamate readily. Finely 
divided platinum when rubbed with mercury in a heated 
mortar produces this amalgam; the amalgamation may be 
facilitated by moistening the platinum with dilute acetic 
acid. 

Iron and platinum unite to form an alloy, and for this 
reason care should be taken not to contaminate platinum with 
iron. The alloy has a lower fusing point than platinum, and 
if iron should come in contact with a platinum piece it will 
result in the fusing of the alloy and thus burn a hole in the 
platinum. 

Iridium and platinum are alloyed to produce an alloy 
possessing rigidity, high fusing point and great resistance to 
the action of chemical agents. The principal uses of this 
alloy in dentistry are for the construction of dowels and bars 
in crown and bridge-work. 

Tin and platinum alloy in all proportions, forming alloys 
which are hard and brittle and more or less fusible. 

Lead and platinum alloy readily, and the alloy has a much 
lower fusing-point than platinum. 

Tin and lead alloys with platinum may be fused in the 
Bunsen burner. When swaging a piece of platinum, using the 
base metals lead or tin, great care should be exercised not 
to contaminate the platinum, for the alloys formed during 
the annealing process would readily fuse and thus ruin the 
piece. 

Melting Platinum Scraps. — As has been already described, 
the oxyhydrogen blow-pipe may be used; it is also claimed 
that the oxyacetylene blow-pipe proves very efficient for 
melting platinum. Dr. Prothero in his late work on Pros- 
thetic Dentistry, describes a method gotten up by Dr. L. E. 
Custer, of Dayton, Ohio, in which the electric current is used. 

There are two forms of melting devices: 1. The current 
from the positive pole is attached to a wire capable of carrying 
a 110-volt current and this is then connected with a carbon 
block, the negative charge is conveyed to a brass electrode 



MELTING PLATINUM SCRAPS 209 

surrounded with a wooden handle. The platinum obtained 
by fusing with this form of a device is harder than new 
platinum because of the absorption of small quantities of 
carbon from the block. 

2. In this form of melting device a lime block is used, a 
piece of heavy platinum wire is so shaped as to form a receptacle 
for the platinum scraps; this wire is attached to the positive 
terminal. The negative terminal is attached to a brass rod 
having a slit in its exposed surface, in which a platinum ingot 
of about one-half ounce weight is fastened. The arc is estab- 
lished by placing a carbon pencil between the terminals. 
(For complete description, see Prothero's Prosthetic Dentistry, 
pp. 1070 and 1071). 

Methods of Separating Platinum, Gold, Silver and Base 
Metals. — If possible, fuse the scrap metal, and while in the 
fused condition pour into water from a height, or the fused 
metal may be rolled out and then cut up into small pieces. 
The object of this procedure is to facilitate the solution with 
aqua regia. The alloy so prepared, or if the scraps are 
infusible in the blow-pipe flame, the original scraps are 
treated with aqua regia (consisting of three parts of hydro- 
chloric acid and one part nitric acid). The reaction should 
be carried out in a porcelain dish of sufficient size to hold the 
excess of aqua regia needed to dissolve the metals. Place 
the dish upon a water-bath and heat, when the reaction has 
ceased, dilute with an equal quantity of distilled water and 
filter. This partially removes silver as the chloride; anti- 
mony and tin as the oxides. Wash the precipitate thoroughly 
with distilled water and then evaporate the solution to dry- 
ness on the water-bath. Dissolve the residue in distilled 
water and allow to stand for a few hours. Any silver remain- 
ing will settle, and by decanting and filtering the silver may be 
completely removed. The gold may be precipitated next by 
warming the solution and adding oxalic acid; filter after the 
gold has been precipitated, and again evaporate to dryness; 
place in a hood and heat for some time to expel the excess of 
oxalic acid. Treat the residue with aqua regia, boil off 
excess of acid then add sodium carbonate solution until the 
14 



210 PLATINUM 

solution is nearly neutral, the platinum may then be pre- 
cipitated by adding ammonium chloride solution. Collect 
the precipitate on filter paper, wash and then heat and the 
platinum will be obtained in the finely divided state. It can 
be fused in the oxy hydrogen blow-pipe flame. 

Resume. 

Symbol, Pt. Crystalline form, isometric. 

Valency, II or IV. Chief ore, iridosmium. 
Atomic weight, 195.2. polyxene. 

Melting point, 1753° C. Conductivity of heat, 84. 

Specific heat, 0.0324. Conductivity of electricity, 
Boiling point, very high 14.6. 

temperature. Coefficient of expansion, 
Malleability, 6th. 0.000008. 

Color, white. Ductility, 1st (3d). 

Tenacity, 3d. Latent heat of fusion, 27.18 
Specific gravity, 21.5. calories 



CHAPTER XVII. 

OSMIUM, IRIDIUM, PALLADIUM, RHODIUM, AND 
RUTHENIUM. 



These metals with platinum comprise the so-called plat- 
inum group. Considering the properties possessed by these 
metals they may be subdivided into two distinct groups. 
Osmium, iridium and platinum consisting one subgroup and 
rhodium, ruthenium and palladium the second. The following 
chart illustrates some of the properties of these metals: 





Atomic 


Specific 


Fusing 






weights. 


gravity. 


points. 


Solubilities. 


Osmium 


. 190.9 


22.48 


2500° C. 


Compact metal insol- 
uble in all acids. 


Iridium 


. 193.1 


22.42 


2300 


Fused metal insoluble 
in all acids. 


Platinum . 


. 195.2 


21.5 


1753 


Solution in aqua regia. 


Rhodium . 


. 102.9 


12.1 


1546 


Insoluble in acids. 


Ruthenium 


. 101.7 


12.26 


next to 
osmium 


Aqua regia with diffi- 
culty. 


Palladium 


. 106.7 


11.5 


1500 


HC1, H2SO4, HNO3. 






OSMIUM. 








Symbol, 


Os. 





Osmium is the heaviest of all bodies. It may be heated 
above the boiling point of platinum without melting when air 
is excluded. When heated to about 415° C. in the presence 
of air the volatile and poisonous perosmic oxide (acid), Os0 4 , 
is formed. In compact form osmium is very hard, cutting 
glass, and possesses a metallic luster resembling zinc in appear- 
ance. It occurs in nature as osmiridium. The metal in com- 
pact form is not attacked by any acid. The precipitated 
metal is slowly dissolved by nitrohydrochloric or fuming 
nitric acids. Osmic acid is used in staining specimens for 
histological work. 



212 OSMIUM, IRIDIUM, PALLADIUM, RHODIUM 

IRIDIUM. 

Symbol, Ir. 

Iridium derives its name from iris, the rainbow, because 
of the color of its various compounds. It occurs as an insol- 
uble compound in the reduction of platinum ores, being 
insoluble in nitrohydrochloric acid. This alloy, osmiridium, 
left after treating the platinum ore with aqua regia, is mixed 
with sodium chloride and heated in a stream of chlorine and 
a double chloride of the metal with sodium results. The mass 
is extracted with boiling water. The solution is then evapo- 
rated and distilled with nitric acid, and osmium is distilled 
off as the peroxide. Upon adding ammonium chloride to the 
solution in the retort iridium is precipitated as ammonium 
chloriridate, (NH 4 )2 IrCl 6 , as a dark, red-brown precipitate, 
and this compound upon heating leaves metallic iridium as a 
spongy mass. Spongy iridium oxidizes readily when heated 
in air, excluding air the iridium may be fused in an oxy- 
hydrogen blow-pipe giving a brittle mass which does not 
oxidize upon heating in air. It is not attacked by aqua 
regia unless in the finely divided state. 

Iridium may also be obtained by treating the platinum 
residues with lead and lead oxide and heating to redness for 
one-half hour. The alloy is then treated with sodium chloride 
and chlorine as described before. 

Properties. — Pure iridium scarcely melts in the oxy- 
hydrogen flame and can be worked only with difficulty; 
however, at red heat it is somewhat malleable. It is rather 
hard metal, having a hardness about equal to slightly tem- 
pered steel. Iridium forms compounds having a valency 
of two, three, and four. The metal combines with carbon 
with the formation of iridium carbide, IrC 4 . The metal in a 
finely divided state dissolves in nitrohydrochloric acid with 
the formation of the chloride. Its best solvent is chlorine. 
When fused with potassium acid sulphate it is oxidized, the 
same results may be obtained by fusing with sodium hydroxide 
or sodium nitrate and the oxide in the latter cases is partially 
soluble in the excess of the alkali. When solutions of iridium 



RHODIUM 213 

salts are treated with formic acid a deep black powder is 
formed. This powder when incorporated with fluxes and 
oils is used as a paint for porcelain work; upon fusing it 
produces a very fine black. 

Iridium is used in springs of fine watches and clocks 
because of its non-magnetic properties. 

Alloys. — Platinum containing a small quantity of iridium 
is rendered more rigid. 

In the laboratory vessels made of this alloy frequently 
scale because of the oxidation of the iridium. Iridoplatinum 
is used in dentistry for dowels in crown and bridge-work 
and also as a means of strengthening continuous gum work. 
The best solder for this alloy is pure gold. Gold alloys with 
iridium, forming a workable alloy, while silver is said to be 
inmiscible with it. An amalgam may be produced, but it 
does not possess any properties of value. 

Compounds. — Iridium forms four oxides: IrO, lr 2 3 , Ir0 2 , 
and IrO. 

Four chlorides are known: iridium dichloride, IrCL?,; 
iridium trichloride, IrCl 3 , and iridium tetrachloride, IrCl 4 . 
Hydrogen sulphide reduces iridium tetrachloride to the 
trichloride and then precipitates the bisulphide Ir 2 S 3 brown, 
soluble in alkali sulphides. 

Stannous chloride, ferrous sulphate and oxalic acid reduces 
iridium to compounds having a valency of three, but does 
not reduce them to the metallic condition. 

RHODIUM. 

Rhodium occurs associated with platinum. It is obtained 
from the solution of the ore in nitrohydrochloric acid by pre- 
cipitating the platinum with ammonium chloride, neutraliz- 
ing with sodium carbonate, adding mercuric cyanide to 
separate palladium, filtering and evaporating the solution 
to dryness in the presence of hydrochloric acid. The residue 
is treated with alcohol and rhodium is obtained as a red 
powder as the double chloride of rhodium and sodium. This 
compound is heated in a tube and a gray powder of metallic 



214 OSMIUM, IRIDIUM, PALLADIUM, RHODIUM 

rhodium is obtained when the residue is washed with water to 
remove the sodium chloride. When fused in the oxyhydrogen 
blow-pipe it becomes a hard, brittle metal. Pure rhodium is a 
white metal said to be nearly as malleable and ductile as 
silver. It may be obtained by being precipitated from solu- 
tion with alcohol or formic acid. 

The pure metal or the alloys with gold or silver is almost 
insoluble in acids; according to Deville and Delroy, the alloys 
with bismuth, lead, copper, or platinum are soluble in nitric 
acid. 

RUTHENIUM. 

According to Gibbs, ruthenium may be obtained from 
platinum ores by mixing the platinum residues with sodium 
chloride then igniting in a stream of chlorine gas. Dissolve 
the fused mass in water and add potassium nitrate, neutral- 
ized with sodium carbonate and then evaporate to dryness, 
extract the double nitrates formed with absolute alcohol, 
this precipitates the rhodium. Add water to the solution, 
distil off the alcohol, and then add hydrochloric acid and the 
ruthenium is precipitated as potassium ruthenium chloride. 
This salt is then converted into the ammonium salt and upon 
adding mercuric chloride upon recrystallizing and igniting 
pure ruthenium is obtained. 

Ruthenium has an exceedingly high melting point. It can 
be melted in the electric arc and it is then a gray and very 
hard metal; though brittle when cold, it becomes malleable; 
when hot it has a specific gravity of 12.26 and is insoluble in 
acids, except nitrohydrochloric in which it is slightly soluble. 

PALLADIUM. 

Symbol, Pd. 

Occurrence. — Palladium is nearly always present in 
platinum ores. It also is found with gold and silver. In the 
native state small quantities are found in Brazil. Palladium 
was at one time extensively used in dentistry for the construc- 
tion of metallic bases for artificial dentures; however, the 



PALLADIUM 215 

price of this metal has advanced so greatly that its use was 
discontinued. 

Reduction. — The native alloys containing palladium is 
fused with metallic silver and then treated with nitric acid 
which leaves gold undissolved. The silver is precipitated by 
adding a chloride and the filtered solution is then treated with 
mercuric cyanide and palladium cyanide is thrown out of the 
solution; when the cyanide is heated spongy palladium is 
obtained. Spongy palladium may be welded into form the 
same as platinum. 

Properties. — Palladium resembles silver in appearance and 
is whiter than platinum. It is softer than platinum and may 
be hammered into sheets or drawn into wire. It conducts 
electricity about one-eighth as well as silver. When the 
metal is slightly heated it assumes a rainbow tint from green 
to violet. In air at the ordinary temperatures, especially 
the spongy form does not tarnish, but at a higher tempera- 
ture, red heat, it becomes coated with an oxide; at a still 
higher temperature the oxide is reduced. 

Hydrogen sulphide does not attack the metal, consequently 
palladium does not tarnish like silver. It may be dis- 
tinguished from platinum by treating with an iodine solution; 
the platinum will not be attacked while palladium forms a 
black compound, Pdl 2 . 

Palladium in spongy form absorbs large quantities of 
hydrogen. It occludes hydrogen even at ordinary tempera- 
tures, and at 100° C. it takes up about nine hundred and sixty 
times its volume of hydrogen. When heated in oxygen it 
takes up this gas which is again given off in the same manner 
as silver under a like condition, and spitting occurs during 
the act of solidification. 

Solubilities. — Boiling hydrochloric or sulphuric acids slowly 
dissolves the metal, while nitric acid, even in the cold, readily 
attacks palladium with the formation of the nitrate Pd(N03)2- 
An alcoholic solution of iodine blackens it, and when fused 
with potassium hydrogen sulphate, palladium is attacked 
with the formation of the sulphate, both of these reactions 
distinguish palladium from platinum. 



216 OSMIUM, IRIDIUM, PALLADIUM, RHODIUM 

Compounds. — Palladium forms three oxides: Pd 2 0, PdO, 
and Pd0 2 . 

Palladium monoxide, PdO, is the most stable oxide of 
palladium. It is formed by gently igniting the nitrate 
Pd(N0 3 ) 2 or by treating palladous chloride, PdCl 2 , with 
sodium carbonate, forming palladous hydroxide, Pd(OH) 2 , 
and then igniting. 

Alloys. — Gold and Palladium. — These alloys are light in 
color and much harder than pure gold. According to 
Prothero the alloys of these two metals which he has investi- 
gated (1 to 30 per cent, palladium) were perfectly uniform, 
malleable, ductile, and tenacious. Silver and palladium 
unite in all proportions, forming exceedingly brilliant alloys. 

Platinum and Palladium.— Platinum and palladium form 
hard alloys which melt below the fusing point of palladium. 

Palladium combines with antimony, bismuth, zinc, tin, 
iron, lead, and nickel. 



CHAPTER XVIII. 
IRON. 

Symbol, Fe (ferrum). Atomic weight, 55.84. 

Occurrence. — Next to aluminum, iron occurs in the great- 
est abundance of all the metals. In the free state iron is 
found present in meteorites. The minerals of iron are of 
importance : 

1. For the extraction of metal (ores of iron). 

2. For the extraction of acid constituents. 

3. For the extraction of metals present as impurities in 
the iron minerals. 

4. For use in their native state. 

The minerals of iron included under (1) and their descrip- 
tions follow: Hematite, specular iron, red iron ore, is the 
principal working ore of iron. It contains about 70 per cent, 
of iron. About 72 per cent, of the iron ore mined in the 
United States is hematite. The hematites are characterized 
by giving a red streak. 

Limonite ranks second, and the cause of this is, it requires 
more fuel to reduce this ore of iron than the hematites. 
Hematites subjected to the influences of water become 
hydrated and their color changes from red to yellow. Limon- 
ites give a yellow streak and may be represented by the 
formula Fe 2 (OH) 6 Fe 2 03. They contain about 59.8 per cent, 
iron. 

Magnetite, Lodestone, Magnetic Iron Ore. — This ore is not 
very prevalent in the United States; however, it is practically 
the only source of iron in Sweden. It produces a very high 
grade of iron, and the noted Swedish steel is manufactured 
from this source of iron. It contains about 72.4 per cent. 

Siderite the carbonate of iron, FeC0 3 , is made use of in the 
production of iron, although it makes up only 1 per cent, 
of the iron ores reduced in the United States. 



218 IRON 

The minerals included under (2) are : (a) For the recovery 
of sulphur. 

Pyrites, FeS2; marcasite, FeS2; pyrrhotite, FenSn+i 

These ores are roasted and the sulphur dioxide is used in 
the manufacture of sulphuric acid. Because of their high 
sulphur content it is generally not considered practicable to 
reduce these ores for their iron. The residues from the roasting 
frequently contain copper, nickel or gold which are recovered 
later. 

(b) For arsenic, arsenopyrite, FeAsS, is the principal 
source of arsenic. 

(c) For chromium, chromic iron, FeCr 2 4 , is the chief 
source of chromium. 

(d) For tungsten wolframite, (FeMn)W0 4 . This mineral 
together with scheelite, (CaWCX), are the principal natural 
occurring compounds of tungsten. 

Minerals Included Under (3). — Gold and silver are recov- 
ered from pyrite and arsenopyrite, and nickel from pyrrhotite. 

Minerals Included Under (4). — The natural oxide paints 
are obtained from this source. Limonite and hematite are 
the principal minerals used. Ochre, umber, sienna are the 
pigments produced. Rouge, used in polishing gold is obtained 
from this source, as is also crocus martis which is used in 
medicine. 

Historical. — Iron, though the most common of metals, 
was in all probabilities not made use of until after the intro- 
duction of gold, silver, copper, tin, and mercury. It is certain 
that it was prepared in ancient Egypt, and at a very remote 
epoch. It was little used in Greece until after the Trojan 
War. The Greeks ascribe the discovery of iron to themselves ; 
but Moses relates that iron was wrought by Tubal-Cain. 
Iron furnaces among the Romans was not fitted with a 
bellows but were located on eminences with the grate in the 
direction of the prevailing winds. The Arundelian marbles 
state that iron was found on Mount Ida, by Doctyles, owing 
to the forests of the mount being burned by lightning, 
B.C. 1432. 



REDUCTION 219 

Mills for rolling and cutting iron were first introduced 
in 1590, and tinning iron in 1681. The first mention of 
casting iron in England was in 1543. Quoting from Dr. 
Ure: "Iron accommodates itself to all our wants and desires, 
and even out caprices. It is equally serviceable to the arts, 
the sciences, to agriculture and war. The same ore furnishes 
the sword, the plowshare, the scythe, the pruning-hook, the 
needle, the graver, the spring of a watch or of a carriage, 
the chisel, the chain, the anchor, the compass, the cannon 
and the bombs. It is a medicine of much virtue and is a 
constituent of both animal, vegetable and mineral kindgom." 

Reduction. — Iron chemically pure is produced by reducing 
pure iron oxide with hydrogen; this is called "iron by 
hydrogen." At the present time practically all iron is pre- 
pared by the blast-furnace process. The crude iron ore is 
first subjected to mechanical treatment, which consists of 
crushing the ore, then the earthy impurities are partially 
removed by w*ashing. 

The washed ore is next roasted; in this process sulphur, 
carbon, and moisture are driven off, and sometimes the ore 
becomes more magnetic. The next process consists of mag- 
netic concentration of the mass; this has a tendency to free the 
ore of earthy impurities which have been broken up during 
the crushing process. The ore may then be treated with 
some binding material and pressed into briquettes and is 
ready for the blast furnace. 

The Blast Furnace (Fig. 51). — The blast furnace consists 
of a vertical shaft, forty to eighty feet high, having the shape 
of a truncated ellipse, with the widest diameter varying from 
ten to twenty-four feet, about one-fourth of the height. At 
the bottom of the furnace is the hearth diameter, four to 
eight feet, in which the molten iron collects; this is perforated 
by several openings or tuyeres, through which the air blast 
enters the furnace. The hearth has also two other openings: 
the lowermost one for the escape of the iron is known as the 
tap hole; the second (slag hole), at a higher level, through 
which the slag is allowed to run out. 

The top of the furnace, called the throat, diameter four 



220 



IRON 



to eight feet, is closed by the bell, which is a cone-shaped 
arrangement for collecting the gases; these then are carried 
away by the downcast and used as fuel for heating the air to 
be used in the blast. 




Operation of the Furnace. — The charge consists of treated 
ore (which must be converted into oxide by roasting if it is 
not a natural oxide), coke, and limestone, (CaC0 3 ). This 
charge is heated in the furnace until reduction is effected 
and the molten metallic iron collects in the hearth of the 
furnace. As reduction takes place the mass sinks into the 
furnace and is replaced by a fresh charge, the ore, coke, and 



PROPERTIES 221 

limestone being introduced in alternate layers. When the 
hearth fills up, the furnace is tapped and the cast-iron runs 
out into troughs molded in the sand. These ingots are 
pigs. Hence the term pig-iron. 

The chemistry of the blast furnace is very interesting. At 
the lower part of the furnace, where the temperature is 
greatest, the burning coal produces carbon dioxide; at the 
middle of the furnace the dioxide is reduced to the monoxide 
by the incandescent coal. In the upper or cooler portion 
of the furnace the monoxide reduces the oxide of iron, 
forming a mass of spongy, metallic iron, as the temperature 
in this part of the furnace is not sufficient to melt the iron; 
but as the latter passes down to the hotter portion it combines 
with a part of the carbon and becomes quite fusible. In the 
hottest part of the furnace some of the silica is reduced to 
silicon, which combines with the carbon and iron to form a 
still more fusible substance known as cast-iron. All of the 
phosphorus and nearly all the sulphur and arsenic go into 
the pig-iron, imparting certain properties to the latter, 
mostly of an undesirable kind. If the ore contains manganese 
oxides, then a part of the manganese will also enter the pig. 

Since about 1900 the electrothermic reduction of iron ores 
has been making rapid progress, due to the fact that very 
high and even temperatures can be obtained. The con- 
tamination of the iron with phosphorus and sulphur so 
frequently contained in the fuels is also eliminated. Ores 
containing titanium can also be smelted in the electric 
furnace, whereas the blast furnace will not develop sufficient 
heat to melt these refractory ores. The Heroult and the 
Keller are the two types of successful furnaces used in this 
method of reduction. The chemical reactions taking place 
within the electric furnace are the same as those occurring 
in the blast furnace. 

Properties. — Iron is a white metal having a specific gravity 
ranging from 7.7 to 8.1. The pure metal melts at about 
1804° C. It is one of the most ductile of metals and is only 
exceeded in hardness by cobalt and nickel. In the finely 
divided state iron burns readily in air when heated, and the 



222 IRON 

iron obtained by reducing with hydrogen may ignite spon- 
taneously upon exposure to air. Upon heating, pure iron 
becomes soft at red heat and as the temperature rises, it 
becomes pasty and may be welded at white heat. Pure iron 
is not acted upon by dry air but in the presence of moisture, 
and especially carbon dioxide, it becomes coated with rust, 
2Fe 2 3 .3H 2 0, and the process which is slow at the beginning, 
proceeds rapidly after a film of oxide has been first formed. 
Iron decomposes water at red heat. 

Solubilities. — Iron dissolves in hydrochloric acid and in 
dilute sulphuric. Concentrated cold sulphuric acid has no 
action, but the hot acid readily attacks iron. 

Dilute nitric acid attacks iron, but the concentrated acid, 
does not dissolve it. If iron is treated with concentrated 
nitric acid, the metal is said to become "passive," and the 
dilute acid will not attack it nor will it precipitate metals 
like copper from solution. 

Finely divided iron possesses the property of combining 
with certain gases, carbon monoxide forming iron carbonyl, 
Fe(CO)5, and when heated with ammonia, iron nitride, Fe 4 N 2 . 

Metallic iron precipitates the free metals from solutions 
of gold, platinum, silver, mercury, bismuth, and copper. 

Compounds. — Iron forms three oxides: ferrous, FeO; ferric, 
Fe 2 3 ; and ferrous-ferric, Fe 3 4 . 

Ferric oxide unites with other metallic oxides, forming 
compounds known as ferrites. Fe 2 3 .FeO would represent 
iron ferrite; Fe 2 3 .CaO, calcium ferrite. 

Ferrous oxide, FeO, is formed when iron oxalate is heated; 
it is a black powder and very unstable, rapidly oxidizing to 
the higher oxides of iron. 

Ferric oxide, obtained by heating ferrous sulphate and by 
quite a few other reactions, is a natural occurring compound 
of iron. 

Ferrosoferric oxide, Fe 3 4 , occurs as magnetite or lodestone. 
When iron is heated in air, this oxide is formed; it is also 
formed when steam is passed over heated iron. 

Ferric Hydroxide. — There are several forms of this com- 
pound; one form, prepared by treating a ferric salt with an 



CAST-IRON 223 

alkaline hydroxide; if this voluminous, brown, gelatinous 
precipitate be treated with ferric chloride it dissolves, and 
upon dialyzing this solution a thick brown liquid is obtained, 
known as "dialyzed iron." 

Iron forms two classes of compounds : ferrous, in which it 
has a valency of two; and ferric, with a valency of three. The 
ferrous compounds are unstable and oxidize to the ferric 
condition. 

Potassium ferricyanide, K e Fe 2 (CN)i 2 , gives a blue pre- 
cipitate with iron in the ferrous condition; this is known as 
"Turnbull's blue." 

Potassium ferrocyanide, K 4 Fe(CN) 6 , produces a blue pre- 
cipitate, Prussian blue, with ferric salts. 

Potassium sulphocyanate, KSCN, produces a red solution 
with iron in the ferric condition. This is an extremely delicate 
reaction, showing the presence of ferric iron 1 part in 1,600,000 
parts of water. 

Iron as obtained from the blast furnace contains impurities; 
it is called pig-iron or cast-iron. 

Cast-iron. — Cast-iron is more fusible and brittle than the 
other forms of iron. It exists in various forms, depending 
upon the impurities present and also the manner in which 
the cast-iron has been cooled. 

Cast-iron is classified in two ways: 

1. According to composition. 

2. According to fracture. 

According to Composition. — Cast-iron in the broadest 
sense is divided into Bessemer and non-Bessemer. Bessemer 
cast-iron contains 0.1 per cent, or less of phosphorus; the 
phosphorus is the limiting agent, although the other elements, 
such as sulphur, manganese and silica are also of some 
importance. 

The non-Bessemer are classed as foundry, basic, mill and 
malleable irons. 

According to Fracture. — This method of classification is 
not used at the present time to the extent it formerly was. 
The pig-iron was dropped upon a wedge-shaped piece of iron 
and examined as to the appearance of the fractured surface. 



224 IRON 

The appearance of the fracture depended upon the condition 
of the carbon. The condition of the carbon is dependent 
upon the temperature of casting, the rate of cooling and the 
silicon content. A change in any of these factors alters the 
nature of the fracture. No. 1 iron is dark gray and its grain 
has large and uniform crystals of graphite to the extreme edge. 
No. 2 has smaller crystals and a little lighter color. No. 3 
is close-grained and lighter in color than No. 2. Mill iron 
shows no grain and the fracture is a dull shade of gray, the 
color depending upon the amount of silicon present. White 
iron, in which nearly all of the carbon is in the combined 
condition, has no market value and is usually resmelted. 

Other alloys formed in the blast furnace are ferrosilicon, 
silicospiegel, ferromanganese, spiegeleisen and ferrophos- 
phorus. They are of importance in the manufacture of steel. 

Wrought Iron. — Wrought iron contains from 0.15 to 0.3 
per cent, of carbon, and under these circumstances has a 
fibrous texture, is very malleable, and its melting point is 
greatly raised (about 1600° C). At very high white heat 
wrought iron becomes liquid, but cannot be cast; there is 
not sufficient fluidity. An addition of 0.5 per cent, of alu- 
minum lowers the melting point sufficiently to make castings 
(ornamental iron work, imitation f orgings) . When the per- 
centage of carbon rises above 0.5 it loses its fibrous texture 
and becomes granular. "Red short" and "cold short" 
are terms applied to wrought iron, meaning that it is weak 
and brittle in either the hot or cold state. Red shortness 
is produced by the presence of sulphur ; cold shortness, by 
phosphorus. Wrought iron is made by the puddling 
process. 

Puddling Process. — The furnace (Figs. 52 and 53) consists 
of a hearth, h, at each end of which there is a fire-brick wall; 
b, the fire-bridge, and d, the flue-bridge. The fire grate is at r. 
The hearth is lined with tap cinder and then a coating one and 
a half inches thick of ferric oxide (fettling). 

Operation of Furnace. — The cast-iron is placed into the 
furnace melted; then well mixed with fettling, (Fe 3 4 ). The 
oxygen of the fettling and of the air removes a large per- 



WROUGHT IRON 



225 



centage of carbon from the iron, with the formation of 
carbon monoxide. The escape of this gas gives to the mass 
the appearance of boiling. When the reaction ceases the 




Fig. 52 




15 



Fig. 53 



226 IRON 

boiling also stops and the iron is removed from the furnace 
and put under the hammer to squeeze out the slag and also 
to condense the porous iron. This operation requires about 
two hours. 

Steel.— This term embraces the varieties of iron which lie 
between cast-iron and wrought iron. 

Steel proper contains only carbon and iron, the former's 
percentage being between 0.4 and 1.5. The production of 
hardness is a direct function of the carbon. All other negative 
elements must be removed down to traces, in order to bring 
out to the fullest the valuable properties of steel. With 0.4 
per cent, carbon the steel is called soft; with 1.5 per cent, 
carbon it is called hard steel. 

The most valuable property is that the carbon can be made 
to change its molecular nature ; so that even the hardest steel 
can become soft. This property is called the temper. Low- 
carbon steel has little temper, while the high-carbon steel has 
the most. The two conditions of the carbon are called (a) 
temper carbon, making steel hard; (b) carbide carbon, making 
it soft. When a piece of steel is heated to redness and 
then allowed to cool slowly (annealed), the carbon all 
becomes carbide variety, the steel is soft. But if the red-hot 
steel is plunged into cold water, the temper variety is 
produced, the steel is hardest. This procedure is called 
tempering. Steel is not as fusible as cast-iron, but more 
fusible than wrought iron, and can be cast as well as welded. 

There are several processes by which steel may be produced, 
the principal ones being the cementation process, crucible 
process, and Bessemer process. 

Cementation Process. — Bars of wrought iron embedded in 
charcoal powder in a suitable chest or converting pot (Figs. 
54 and 55) made of some substance capable of resisting fire 
are, after from seven to ten days' exposure to heat, converted 
into steel, the iron taking up the requisite amount of carbon. 
The product of this operation is called blistered steel, and 
is far from uniform,, either in composition or texture, as 
portions of the bars thus produced will be found to contain 
more carbon than others and the interior to be more or less 



STEEL 



227 



porous. For the purpose of improving its quality, the bars 
are cut into short lengths, made up into bundles' heated to 
the welding point, and placed under a powerful tilt hammer, 




Fig. 54 




Fig. 5.", 



228 IRON 

which consolidates each bundle into one mass. This is called 
shear steel. 

Crucible Process. — Fusing and casting steel is another 
process for the treatment of the blistered form, by which is 
produced the best and most homogeneous variety. It con- 
sists in fusing about thirty pounds of broken fragments of 
blistered steel in a plumbago crucible, the surface being 
protected from oxidation by glass melted upon it. When 
perfectly fluid the steel is cast into ingots, and when it is 
desirable to form a very large ingot several crucibles are 
simultaneously emptied into the same mold. Cast-steel 
is superior in density and hardness to shear steel, and is the 
form best adapted to the manufacture of fine cutting instru- 
ments. It is, however, somewhat brittle at red heat, and 
much care and skill are required in forging it. The addition 
to it, while fused, of one part of a mixture of charcoal and 
oxide of manganese affords a fine-grained steel, which may 
be cast into a bar of wrought iron in the ingot mold, in 
order that the tenacity of the iron may be an offset to the 
brittleness of the steel when forged together, while it affords 
an economical compound in the manufacture of cutting 
implements, the iron forming the back and the steel the edge 
of the instrument. 

Electrothermic Process. — Heroult has also invented an 
electric furnace for steel making. The charge may be either 
all pig-iron, or part pig-iron and part steel scrap, which is 
melted upon the hearth of the furnace, or the pig-iron can be 
melted first and then poured upon the hearth. The operations 
of treating and refining are similar to those of the basic open 
hearth furnace, except that the heat is produced by electricity 
instead of gas. The advantages of the Heroult furnace over 
the open hearth are that any desired temperature can be 
obtained and therefore a greater variety of slags and fluxes 
can be used, facilitating the removal of certain impurities. 
The contamination of the steel with impurities from fuel 
combustion are also avoided. 

Other furnaces (Ivjellin, Colby and Gin) for accomplishing 
the same result, but embodying different principles, have also 
been constructed. 



STEEL 



229 



Bessemer Process. — Bessemer steel is produced by forcing 
atmospheric air into melted cast-iron which is free from 
phosphorus and sulphur. The oxygen first takes hold of the 
silicon, burning it to Si0 2 ; then it burns the carbon, which is 
oxidized more readily than the iron, forming carbon monoxide, 
combustion of which takes place on coming in contact with 
atmospheric air, and sufficient heat is thus generated to keep 
the temperature above the melting point of steel during the 
operation. The current of air is stopped as soon as the 
decarburation has been completed, when a quantity of white 
pig-iron containing manganese (ferromanganese or spiegel- 
eisen) is added to the fluid metal for the purpose of assisting 
the separation of gas from the melted metal and to impart 
the requisite amount of carbon. It is then ready for casting. 




This process is carried out in the so-called Bessemer con- 
verter (Fig. 56), which is an egg-shaped vessel made of 
wrought iron and lined with gannister, which is an infusible, 
silicious rock. The bottom of the converter forms the tuyere 



230 IRON 

box through which the air blast enters the converter. If the 
iron contains phosphorus it must be treated in one of two 
ways: 

(a) Acid Bessemer process, if the pig-iron contains only 
traces of phosphorus. The converter is lined with brick made 
from pulverized quartz (hence acid). Special ores, so-called 
Bessemer ores, are used in this method. 

(6) Basic Bessemer process is used if the pig-iron contains 
much phosphorus, up to 3 per cent., but is low in silicon. 
Such pig can be made from cheaper ore. The vessel is lined 
with brick made from magnesite, (MgC0 3 ), under high 
pressure. 

Hardening and Tempering. — Four kinds of hardness in steel 
must be recognized, viz. : non-crystal hardness ; crystal hard- 
ness; refractory hardness of alloy steel; density hardness 
produced by hammering. 

Non-crystal hardness is produced by heating the metal 
and suddenly chilling it in water, wrought iron absorbing 
about 1 per cent, of carbon and combining with it, forming 
an iron carbide (austentite) . This carbide is very unstable. 
Overheating causes the mass to crystallize, and thus degener- 
ate. Reheating the hardened steel to almost 500° F. causes 
the ferrite (iron) to be set free. 

Crystal hardness is usually caused by overheating to the 
point where the grain previously made dense by hammering 
or rolling is again opened, thus enlarging the artificially fine 
crystals. The finer the steel the greater will be the loss of 
hardness and strength through crystallization. 

Refractory hardness is produced in steel by alloying it 
with some refractory metal which only melts at some extra- 
ordinarily high temperature and part of which property the 
steel acquires, not only chemically, but also physically. 

Hardening of ordinary carbon steel is effected by subjecting 
the object to extremes of temperature. The common practice 
is to first coat the surface of the metal with some carbonaceous 
substance, such as soap, to prevent scaling and oxidation 
of the surface. Ferrocyanide of potassium has also been used 
for surface hardening. This salt contains cyanogen, (CN), 



STEEL 231 

a gas consisting of twelve parts by weight of carbon and 
fourteen of nitrogen. This is decomposed at the high tem- 
perature which is employed, and supplies carbon to the 
surface of the metal. This salt is, however, better suited 
to the process known as case-hardening, while in retempering 
dental instruments soap answers every requirement. 

The metal is next heated to the point of full redness, and 
then suddenly plunged into cold water, oil, tallow, or mercury, 
or, in the case of small objects, is merely placed on a large 
piece of cold metal. It is thus rendered very hard, while at 
the same time it increases slightly in volume. 

If hardened steel be heated to redness and allowed to 
cool slowly it is again converted into soft steel, but it may be 
proportionately reduced by heating to a temperature short 
of redness, the proper point of which may be ascertained 
by noting certain colors which appear on the ground or 
brightened surface of a steel instrument when held over a 
flame. This discoloration is due to the formation of a thin 
film of oxide, and as the temperature rises the film becomes 
thicker and darker and the instrument softer. It is therefore 
necessary to plunge the instrument into a cold menstruum 
the instant the color indicating the desired degree of hardness 
is reached. The following table indicates the tempering 
heats of various instruments: 



Temperature. 


Color. 


Use. 


217° to 232° C. 


Light yellow. 


Enamel chisels. 


243° a 


Medium yellow. 


Excavators. 


258° C. 


Brown yellow. 


Pluggers. 


266° C. 


Brown purple. 


Saws, etc. 


271° C. 


Purple. 


Wood-cutting tools. 


277° to 299° C. 


Blue. 


When elasticity is desired 



A molten alloy of tin and lead in varying proportions can 
also be used to supply a uniform heat. 

In "letting down" or tempering dental instruments the 
flame of a spirit lamp may be employed, the instrument being 
placed in it; the flame should strike, however, some distance 
from the cutting end, and when the proper color reaches the 
end it should be thrust into water. Another very convenient 
means of effecting the same result consists in heating an iron 



232 IRON 

bar to redness at one end and then fixing it in a vise. The 
object to be tempered is placed in contact with this until the 
desired tint appears. 

Steel when fractured shows a fine silky appearance of the 
broken surface. Overheating, however, deprives it of carbon, 
when the fractured surface presents a coarse, granular 
condition, showing that it is unfit for use for fine cutting 
instruments. 

A steel instrument may be readily distinguished from one 
of iron by placing a drop of nitric acid upon it, a dark stain 
being produced upon steel by the separation of the carbon. 

Alloys of Steel. — By alloys of steel are meant those 
steels that owe their special properties to the presence of 
other elements other than carbon. 

Copper Steel. — The alloys of copper and steel are noted 
for their property to resist the action of corrosion. A product 
recently placed upon the market known as "Vismera," is 
said to be highly resistant to the action of agents which 
ordinarily corrode steel. This alloy contains about 0.2 per 
cent, of copper. Higher alloys containing from 5 to 20 per 
cent, of copper are said to possess great strength, tenacity 
and malleability. 

Harveyized Steel. — Harveyized steel is steel heated to 
about the melting point of cast-iron and then the surface of 
the metal treated with carbon. The carbon percentage in 
the steel is raised about 1 per cent., and then plunged into 
water and cooled. The surface of the steel so treated is 
extremely hard and resistant and is used for armor plate. 

Aluminum Steel. — The addition of aluminum slightly 
increases the tensile strength and proportionately the elas- 
ticity, in rolled and cast-steel when the amount added is 
not greater than 1 per cent. 

Aluminum is also added to molten steel, especially when 
the mass has been chilled so that it will not pour readily; 
the aluminum reduces the fusing point of the steel and thus 
assists in the pouring. 

Chrome Steel. — Chrome steel contains from 1.5 to 2 per 
cent, of chromium, generally added as ferrochrome. This 



STEEL ■ 233 

steel possesses hardness and tensile strength, but interferes 
with the welding. It is used sometimes for tools but mainly 
for giving very hard surfaces and resistance to severe shocks. 

Nickel Steel. — This steel usually contains from 5 to 30 
per cent, nickel. This is a very useful alloy of steel because 
of the physical properties which it possesses. It is said to 
increase the strength of steel about 50 per cent., less liable 
to corrode; besides these properties it also adds to the life 
of the alloy, as it has about six times the resistance to fatigue. 

The presence of small quantities of manganese in nickel 
steel is most important, as it appears that without the aid of 
manganese in proper proportions the best results could not 
be obtained. 

This steel works readily hot or cold, forges easily, and 
machines harder than carbon steel. 

Manganese Steel. — Depending upon the quantity of man- 
ganese present the physical properties of this steel are brittle 
or extremely tough. With a low content of manganese, 
say 1.25 per cent., a very brittle unworkable product is formed; 
however, an alloy containing from 7 to 14 per cent, is very 
peculiar. It possesses extreme hardness and toughness. 
It is so hard that castings made from it are not touched by 
the file, yet it may be hammered like the softest of mild 
steels. It possesses non-magnetic properties and is used on 
this account in the construction of dynamos. 

Tungsten (Musket Steel). — Tungsten steel is produced by 
alloying a certain percentage of tungsten with steel. If from 
3 to 3.5 per cent, of metallic tungsten is melted together 
with low-carbon steel, an alloy results which does not need 
tempering; it turns hard even on slow cooling (air-quenched 
steel) . It is sometimes quenched by blowing a blast of air, 
which gives it greater hardness than if allowed to cool in 
quiet air. If the alloy be plunged in oil or water to quench 
it, it becomes so hard that the strain overcomes the cohesion 
of the molecules and cracking results. This alloy is used as a 
so-called "high-speed tool steel." It can be used in lathes 
and boring mills, and the heat produced in no way affects 
the temper of the steel, thus causing a great saving of time. 



234 



IRON 



Vanadium Steel. — Carbon steel or alloy steels generally 
contain from 0.1 to 1 per cent, of vanadium. It is claimed 
that this element acts by removing dissolved gases, especially 
nitrogen, with the result that the greater part of vanadium 
is eliminated in the slag. However, the vanadium remaining 
in the steel greatly modifies its microscopic appearance. 

Vanadium has little virtue if used alone, but when com- 
bined with other elements acts very beneficially. 

High-speed Steels. — High-speed steels so-called on account 
of the great rapidity with which they machine metals. They 
usually contain under 1 per cent, carbon, from 12 to 24 per 
cent, tungsten, and 0.3 per cent, manganese. Sometimes the 
tungsten is replaced by 10 per cent, of molybdenum. These 
steels will retain their toughness and hardness at a red heat, 
and therefore tools made from them can be run at such a 
high rate of speed that they will become red hot from friction. 
High-speed steel is tempered by heating to about 1100° C, 
and cooling by blowing a blast of cold air upon it. 



Resume. 



Symbol, Fe. 
Valency, II or III. 
Atomic weight, 55.84. 

Cast 1250 c 



Melting point 



to 
1300° C. 
Pure 1600° to 
1804° C. 
Specific heat, 0.1138. 
Boiling point, 2450° C. 
Malleability, 9th. 
Color, bluish. 



Tenacity, 1st. 
Specific gravity, 7.7 to 8.1. 
Crystalline form, isometric. 
Chief ore, hematite. 
Conductivity of heat, 120. 
Conductivity of electricity, 

17.5. 
Coefficient of expansion, 

0.000012. 
Ductility, 4th. 



CHAPTER XIX. 
ALUMINUM. 

Symbol, Al. Atomic weight, 27.1. 

Occurrence. — Aluminum of all the metals, occurs in the 
greatest abundance. The native metal is not found in nature. 
In the combined condition it is present in many silicates and 
is an essential constituent of all clays. 

The aluminum minerals may be classed: (1) Ores of 
aluminum, (2) abrasive materials, (3) gems. 

Ores of aluminum, bauxite, Al 2 0(OH) 4 , gibbsite, A1(0H) 3 , 
are the principal ores of aluminum. 

Abrasive materials, corundum, A1 2 3 . This substance 
ranks next to the diamond in the scale of hardness. Emery 
has the same composition with a small amount of oxide of 
iron as impurities. These materials were used extensively 
as abrasives until the introduction of carborundum, which 
is an artificially prepared carbide of silicon, SiC. Cryolite, 
Xa 3 AlF 6 , the sodium aluminum fluoride is of importance in 
the reduction of aluminum. 

Reduction. — Before the introduction of the electrolytic 
process most of the aluminum was prepared by the following 
method : 

Bauxite is first freed from iron: 1. The powdered bauxite 
is mixed with sodium carbonate and heated in a reverberatory 
furnace. 

AI2O3 + 3Na 2 C0 3 = Al 2 03,3Na 2 + 3C0 2 . 

2. The sodium aluminate is extracted with water, leaving 
the iron as an insoluble oxide. Carbon dioxide is passed 
through the filtered solution, decomposing the sodium 
aluminate. 

Al 2 3 ,3Na 2 + 3H 2 + 3COa = 3Na 2 COs + A1 2 3 ,3H 2 0. 



236 ALUMINUM 

3. The purified oxide of aluminum is dried and mixed with 
sodium chloride and powdered wood charcoal. Water is 
then added to the mass which is then worked up into balls. 
These are dried at 150° and then packed into a fire-clay 
cylinder and strongly heated in a stream of chlorine: 

AI2O3 + 3C + 3C1 2 = 3CO + 2AICI3. 

The aluminum chloride combines with sodium chloride 
and volatilizes from the retort. It is collected in earthenware 
receivers and represents the aluminum entirely freed from 
iron. 

4. The double chlorides are then reduced by metallic 
sodium. The charge is introduced into a heated reverbera- 
tory 'furnace and a violent reaction occurs; after a short 
time metallic aluminum separates out beneath the slag and is 
collected. Cryolite is used as a flux in this reaction. 

Al 2 Cl 6) 2NaCl + 6Na = 2A1 + 8NaCl. 

The chemical processes are now largely replaced by the 
electrolytic ones. 

The Heroult and the Cowles processes both depend upon 
electrolysis, but they only are adapted to the making of 
aluminum bronzes. Although antedating the Hall method, 
they cannot be used for making pure aluminum. 

The Hall Process. — In this process advantage is taken of 
the solvent action of cryolite for bauxite. This solution 
conducts an electric current and the cryolite is not decom- 
posed, wit^h the result that aluminum is freed from its 
combination with oxygen. 

The other solvents for bauxite which were used in the past 
would be decomposed by the current before the oxide of 
aluminum would be attacked. The vessels or pots employed 
in this process are rectangular iron boxes, thickly lined with 
carbon. The carbon lining constitutes the cathode. The 
anodes consist of carbon cylinders, and are supported above 
the pots, dipping into the bath of fused fluorides. No external 
heat is employed, the heat developed by the resistance to the 
current being all that is necessary to maintain fusion. 



PROPERTIES 237 

Aluminum is added from time to time as required. The 
process proceeds quietly, the resistance offered by the bath 
charged with alumina being very low, but the moment the 
alumina is exhausted the resistance increases fourfold. In 
order that the workmen may be made aware of the state of 
the bath, an incandescent lamp is attached to each bath, 
which emits no light during the low resistance, but shines 
brightly when the resistance and consequently the electro- 
motive force at each bath increases sufficiently; so whenever 
one of the incandescent lamps begin to shine the workmen 
hasten to stir in a fresh supply of alumina. The process 
proceeds quietly day and night. It is only necessary to keep 
the baths supplied with alumina, and every twenty-four 
hours tap the pots and draw off the metal. There are over 
one hundred of these pots altogether, and the yield is about 
one hundred pounds of aluminum per pot every twenty-four 
hours, or about ten thousand pounds altogether. 

Properties. — Aluminum is a white metal, odorless and taste- 
less, very ductile and malleable. It is about as hard as silver. 
The specific gravity of aluminum is about 2.56 and it is the 
lightest of the metals in common use. 

Commercial aluminum is never pure and a product purer 
than 99.75 per cent, is rarely obtained even in purified 
varieties: generally containing silica, iron and sometimes 
lead or copper. It crystallizes in octohedrons. It fuses at 
654° C, and requires an extremely high temperature to 
volatilize, about 1800°. Like zinc, aluminum is best rolled 
between 100° and 150°. It may be rolled or hammered out 
into foil and is also obtained in the powdered form. 

Powdered aluminum possesses a great affinity for oxygen, 
taking the oxygen from combination with other metals and 
liberating an intense heat. It possesses the property of 
sonorousness to a remarkable extent, more so than any other 
metal. 

Aluminum is unaltered by the air, even in the presence of 
moisture. When heated in thin sheets in a current of oxygen 
it burns and is converted into the oxide. It conducts an 
electric current about one-half as well as copper and conducts 



238 ALUMINUM 

heat about two-thirds as well as silver. When molten it 
possesses great fluidity but because of its lightness is rather 
hard to cast by simply pouring. For commercial purposes 
zinc is added to aluminum to aid in the casting process. 

Aluminum is used in the construction of dental bases for 
artificial dentures, and depending upon the method of con- 
struction there are two varieties of aluminum bases : (a) cast ; 
(b) swaged. 

Cast Aluminum Bases. — The objections to aluminum in 
this class of work are: (1) warpage; (2) lack of density of the 
cast aluminum; (3) reaction of the fluid of the mouth upon 
the metal. Warpage results from two causes, i. e., changes in 
the investment and also contraction of the aluminum during 
solidification and cooling. Dr. H. J. Goslee, in an article 
published in the Dental Review, August, 1914, suggests an 
indirect method of casting. The object of this method of 
casting is to correct any warpage by a subsequent swaging. 
Richards states that to overcome the difficulties of contrac- 
tion and corrosion by the fluids of the mouth Dr. Carroll 
adds a little copper, which, he says, decreases the contraction 
while the addition of some platinum and gold renders it 
unalterable in the mouth. 

Cast aluminum, under the microscope appears irregular 
upon its surface, and the presence of organic acid or alkalies 
may find points of lodgment in these irregularities, causing a 
dissolution of the aluminum. For this reason cast aluminum 
is not as resistant to the fluids of the mouth as it should be. 

As aluminum was used in the past the metal was supposed 
to contain sufficient quantities of iron, as a result of this a 
voltaic couple was formed, causing a solution of the aluminum. 
Dentures were frequently seen in which small holes had 
been found completely penetrating the denture. 

Aluminum is generally annealed by coating its surface with 
sweet oil or vaseline and then igniting; when the last trace 
of carbon burns from the surface the metal is quickly plunged 
into water. If the metal be held in the free flame it frequently 
happens that a portion of it will fuse. 

In melting small chips of aluminum or those of its light 



PROPERTIES 239 

alloys only about 30 per cent, of the metal melts. It was 
discovered that by adding small quantities of anhydrous 
aluminum chloride, A1C1 3 , 50 to 60 per cent, was melted. 
By two or three operations of this kind a 70 per cent, melt is 
possible. 

Swaged aluminum dentures are supposed to possess greater 
density due to the mechanical treatment to which the alu- 
minum has been put to. There is a difference of opinion as to 
which form of aluminum denture possesses the greatest 
lasting powers. Pr other o points out the fact that 26-gauge 
aluminum, which is the form mostly used in this work, is 
only about one-third the thickness of the average cast-plate, 
consequently the age of a cast-plate should exceed that of a 
swaged one. 

For some time the difficulty of soldering aluminum pre- 
vented the metal from being applied to useful purposes. The 
solder recommended for general use in the manufacture of 
articles of ornamentation is composed of copper, four parts; 
aluminum, six parts; zinc, ninety parts. The use of this 
requires some skill and experience. At the moment of fusion 
small aluminum tools are used, the friction of which is 
necessary to induce adhesion. Borax cannot be employed 
as a flux, as it is liable to attack the metal and prevent union. 

Another method of uniting two pieces of aluminum with 
ordinary solder in conjunction with silver chloride as a flux 
has recently been recommended by F. J. Page and H. A. 
Anderson, of Waterbury, Conn. The finely powdered fused 
silver chloride is spread along the lines of junction, and the 
solder is melted with a blow-pipe or other device. The union 
thus obtained is said to be perfectly strong and reliable. 1 

The following alloys are also used as solders in unalloyed 
aluminum articles of jewelry: 

I. II. III. IV. 

Zinc 80 85 88 92 

Aluminum 20 15 12 8 

In soldering with these alloys a mixture is used as a flux 
consisting of three parts of copaiba balsam, one part of 

1 Chemical News, iv, 81. 



240 ALUMINUM 

Venetian turpentine, and a few drops of lemon juice. The 
soldering iron is dipped into the mixture. 

Mr. William Frismuth, of Philadelphia, recommends the 
following solders for aluminum, with vaselin as the flux: 

Soft Solder. 

Pure block tin from 90 to 99 parts 

Bismuth from 1 to 10 parts 

Hard Solder. 

Pure block tin from 90 to 98 parts 

Bismuth " 1 to 5 " 

Aluminum " 1 to 5 i! 

Schlosser 1 recommends two solders containing aluminum 
as especially suitable for dental laboratory use: 

Platinum-aluminum Solder. 

Gold 30 parts 

Platinum 1 part 

Silver 20 parts 

Aluminum 100 " 

Gold-aluminum Solder. 

Gold 50 parts 

Silver 10 " 

Copper 10 " 

Aluminum 20 " 

i 

Solubilities.— The best solvent for aluminum is hydro- 
chloric acid. 

2A1 + 6HC1 = A1 2 C1 6 + 3H2. 

When heated with strong sulphuric acid aluminum dissolves 
with the liberation of sulphur dioxide: 

2A1 + 6H2SO4 = A1 2 (S0 4 )3 + 3S0 2 + 6H2O. 

Nitric acid, dilute or concentrated, does not attack 
aluminum. Organic acids in the presence of sodium chloride 
attack aluminum. 

A 4 per cent, solution of acetic acid even in the presence of 

1 Richards, 



ALLOYS 241 

sodium chloride has very little action on this metal and when 
the above mixture was heated for fourteen hours, only one 
part of aluminum in five hundred and twenty-six parts of the 
acid was found. 

Sodium and potassium hydroxides attack aluminum with 
the formation of aluminates and hydrogen. 

2A1 + 2KOH + 2H 2 = 2KAIO2 + 3H 2 . 

Powdered or leaf aluminum when boiled with water 
decomposes it with the evolution of hydrogen. 

2A1 + H2O = 2A1(0H) 3 + 3H 2 . 

Compounds. — Oxide, A1 2 3 , occurs native in a colorless 
crystalline condition as corundum, and colored by traces 
of various metallic oxides in the precious stones such as 
ruby, sapphire, and amethyst. In less pure conditions it occurs 
in large quantities as emery. It may be prepared in an 
amorphous condition by igniting the hydroxide, nitrate, and 
various other salts of aluminum. 

Aluminum hydroxide, Al(OH) 3 , is prepared by treating a 
solution of an aluminum salt with ammonium hydroxide. 
Aluminum hydroxide is capable of acting as a feeble acid 
oxide; thus, the hydroxide is dissolved by sodium or potas- 
sium hydroxide with the formation of aluminates. 

Al(OH) 3 + 3 NaOH = Al(ONa) 3 + 3 H 2 0. 

Alloys. — When mercury comes in contact with a polished 
aluminum surface, the surface immediately becomes dull, 
and a moss-like growth of aluminum hydroxide arises upon 
the surface. The aluminum amalgam first formed is decom- 
posed because the aluminum in the amalgam is attacked 
by the oxygen of the air. 

E. Kohn states that aluminum amalgam may be prepared 
by dipping aluminum into a solution of mercuric chloride; 
this amalgam oxidizes with the evolution of hydrogen from 
the solution. 

It has been suggested that this amalgam may be used to 
free water from coloring matter ,as it precipitates tannates 
18 



242 ALUMINUM 

from solution. Copper present to the extent of 0.1 percent, 
is said to prevent the decomposition of this amalgam. 

Aluminum Bronze. — Aluminum and copper readily alloy, 
and alloys containing up to 15 per cent, of aluminum 
possess hardness, do not tarnish and possess increased 
tensile strength. The color closely resembles gold, and it is 
sometimes used for souvenir metals. 

The following solders are well adapted to aluminum bronze : 

I. Hard Solder for 10 Per Cent. Aluminum Bronze. 

Gold 88.88 per cent. 

Silver 4.68 

Copper 6.44 

100.00 

II. Medium Hard Solder for 10 Per Cent. Aluminum Bronze. 

Gold 54.40 per cent. 

Silver 27.00 

Copper 18.00 

100.00 

III. Soft Solder for Aluminum Bronze. 

^° n pper ™ pC V ent - } Brass 14.30 per cent. 

Gold 14.30 

Silver 57.10 

Copper 14.30 

100.00 

For a flux: "Gaudin's liquid flux" consisting of pulverized 
cryolite and phosphoric acid dissolved in alcohol. 

Aluminum and copper: Fenchel states that with a high 
percentage of gold these alloys are hard and brittle. 

Zinc and tin also form brittle alloys with aluminum. 

Silver and aluminum form alloys, and in the presence of 
4 per cent, silver an alloy is obtained which may be more 
readily worked with a file than pure aluminum. Petrenko 
claims a 7 per cent, silver alloy will not tarnish upon exposure 
to the air. 

Nickel forms several compounds with aluminum. 



RESUME 



243 



Resume. 



Symbol, Al. 
Valency, III. 
Atomic weight, 27.1. 
Melting point, 654.5° C, 
Specific heat, 0.2143. 
Boiling point, 1800° C. 
Malleability, good. 
Color, Avhite. 
Specific gravity, 2.56. 



Crystalline form, octa- 

hedrals. 
Chief ores, bauxite. 
Conductivity of heat, 5th. 
Conductivitv of electricity, 

63. 
Ductility, 8th. 
Coefficient of expansion, 

0.00002313. 
Tenacity, good. 



CHAPTER XX. 
ZINC. 

Symbol, Zn. Atomic weight, 65.37. Valency, II. 

History. — Zinc was known to the ancient Greeks under the 
name of cadmia and was used in the manufacture of brass. 
There is no record of the method used by them in reducing 
zinc ores. Until the eighteenth century the zinc of Europe 
was imported from China. 

So far as can be ascertained this metal was discovered by 
the moderns. It is said, however, to have been known in 
China, and is noticed by European writers as early as a.d. 
1231, though the method of extraction was not known until 
five hundred years after. A mine in Yorkshire, England, 
was discovered in 1809. This date may be considered as the 
starting point of the modern industry as it is known today. 
The name zinc was given to the metal by Paracelsus in the 
sixteenth century. 

Occurrence. — Missouri, Kansas, Indiana and Illinois, yield 
most of the zinc ores of the United States; although other 
important deposits exist in Pennsylvania, New Jersey, and 
Virginia. 

The principal sources of zinc in Europe are located in 
England, Hungary and Silesia. Zinc, as a rule, does not exist 
in the free state in nature, although it is claimed that the 
native metal has been found near Melbourne, Australia. 

The principal ores are: sulphide, sphalerite, (ZnS); oxide, 
zincite or red zinc, (ZnO) ; carbonate smithsonite or calamine, 
(ZnC0 3 ); silicates willimite, (Z^SKX); calamine, (ZnOH) 2 , 
Si0 3 ; oxide franklinite or horseflesh ore, (FeMnZn) 3 4 . 
Zinc carbonate is also known as zinc blend. Blend is 
derived from the German, meaning to dazzle, which refers 



REDUCTION 



245 



to the brilliancy of the crystals, which are almost black, due 
to the presence of iron sulphide. 

Reduction. — The ore is first roasted in a reverberatory 
furnace; then distilled, mixed with charcoal, in closed 
earthen or iron vessels. The roasting converts the carbonate 
or the sulphide into the oxide: 



ZnCOs 

2ZnS ■ 



- heat 
30 2 



ZnO + CO2 
2ZnO + 2SO2. 



The charcoal reduces the oxide and the free zinc distils 
over into the receivers. 

ZnO + C = Zn + CO. 




Fig. 57 



The process varies in different countries; in Silesia, 
Germany, fire-clay muffles are used, this is known as the 
Silesian process (Fig. 57); in Belgium, earthenware tubes, 
Belgian process (Fig. 58) ; and in England, fire-clay retorts. 
The English furnace is conical in shape, having an interior 
dome; six crucibles are placed within the furnace, each has a 
hole in the bottom, through which an iron pipe passes to 
convey the zinc vapor. After placing the charge of zinc oxide 



246 



ZINC 



and coke in the crucible, the top is cemented into place and 
the crucibles are heated until a bright red heat is obtained. 
The first portions of the gas from the iron tubes are com- 
monly very impure, containing cadmium and arsenic and the 




Fig. 58 



gases burn with the so-called "brown blaze;" but when the 
"blue blaze" begins, that is, when the metallic vapor burns 
with a bluish- white flame, the zinc is collected in suitable 
vessels placed beneath. The reduced zinc is afterward 
cast into ingots; this product is impure zinc, known as 



PHYSICAL PROPERTIES 247 

spelter, and contains generally iron, cadmium, lead, copper, 
carbon and arsenic as impurities. 

Physical Properties. — Zinc is highly crystalline in nature, 
having a brilliant lamellar crystalline structure upon fracture. 
It does not tarnish in dry air and is only slowly acted upon 
even in moist air with the superficial formation of the 
carbonate. 

Specific gravity, 6.861 (cast) to 7.142 of the rolled varieties. 

Melting point, 415° C, 779° F., below red heat. 

Boiling point, variously stated from 916° to 1040° C, or 
1681° to 1742° F. When heated to a bright red heat with 
excess of air, zinc burns with a bluish-white flame with the 
formation of a white flocculent substance, ZnO, resembling 
wool and formerly known as philosopher's wool. At ordinary 
temperature it breaks with a crystalline fracture, but when 
heated to a temperature from 100° to 150° C, it becomes 
malleable and at these temperatures may be rolled into 
sheets or drawn into wire. Zinc so heated retains its mallea- 
bility at ordinary temperature. Above 150° or about 205° C, 
it again becomes brittle, and at a temperature just below its 
fusing point it is so brittle that it may be pulverized in a 
mortar. Conductivity of heat, 303; conductivity of elec- 
tricity, 5.751 or about fourth. It ranks eighth in malleability 
and sixth in ductility. Zinc is frequently used in the con- 
struction of a voltaic cell because of its position in the electro- 
motive series. Zinc precipitates nearly all metals from solu- 
tion and is itself precipitated by magnesium in an acetic 
solution. Zinc posseses a rather high degree of expansibility, 
and is consequently used for the purpose of making dies 
for swaging metal plates for artificial dentures. By many 
dentists it was formerly thought that a metal, to be well 
suited for this purpose, should be entirely destitute of this 
property, so that after casting the die should not, in returning 
to its former condition in cooling, be smaller than the plaster 
model, the object per se being to have the plate fit the plaster 
cast perfectly; whereas, the real purpose should be to make 
the plate fit the mouth closely, the plaster model being only 
a means to the end. Plaster expands in setting. From the 



248 ZINC 

impression to the model two expansions are gone through 
before the facsimile of the mouth in plaster is obtained; 
hence a plate made to fit such a model perfectly must 
necessarily be somewhat larger than the mouth — a condition 
unfavorable to atmospheric adhesion. On the other hand, a 
plate to fit the zinc will not be found too small for the mouth, 
but will, provided the impression is a good one and represents 
perfectly the conformation of the mouth, afford a very close- 
fitting plate. Even better results might be expected where 
the plate is somewhat smaller than the mouth, because such 
a condition would, in entire upper dentures, throw any 
undue pressure upon the alveolar ridge, while that portion 
of the plate covering the palatine arch would barely be in 
contact with the tissues; the pressure along the ridge would 
quickly promote absorption of the alveoli, and a uniform 
adaption of the plate to the mouth would soon follow. On 
the contrary, if the plate be made to fit the plaster cast, and 
is a trifle larger than the mouth, the pressure will be thrown 
upon the palatine arch at the back edge of the plate, at a 
region not likely to change by absorption, as is the case with 
the alveolar ridge, and hence the margin of the plate will 
embed itself in the tissues and cause much discomfort and 
impair the usefulness of the denture. 

Much time and thought have been expended in the effort 
to discover some alloy which, in connection with the prop- 
erties of hardness and fusibility, shall possess that of non- 
expansibility when heated. Harris's Principles and Practices 
of Dentistry gives no less than nine different formula?. The 
author is satisfied that the property of expansibility in zinc 
as used in the dental laboratory constitutes one of its most 
valuable qualities, as it gives us the means of compensating 
for the yielding of the tissues and the absorption along the 
ridge which nearly always follows the first insertion of an 
artificial denture. 

Solubilities. — Pure zinc dissolves very slowly in acids or 
alkalies unless in contact with copper, platinum or some less 
positive metal. The metallic impurities in ordinary zinc 
enables it to dissolve easily with acids or alkali hydroxide. 






ALLOYS 249 

In contact with iron, it is quite rapidly oxidized in water 
containing air, but not dissolved by water unless by aid of 
certain salts. It dissolves in dilute hydrochloric, sulphuric 
and acetic acids. 

Zn + H2SO4 = Z11SO4 + H 2 . 

With aqueous solutions of the alkalies, zincates are formed: 

Zn + 2KOH = K2Z11O2 + H 2 . 

Nitric acid attacks it with the formation of zinc nitrate, 
and depending upon the strength of the acid, ammonium 
nitrate, nitrous oxide, or nitric oxide is formed. 

4Zn + IOHNO3 = 4Zn(N0 3 ) 2 + NH4NO3 + 3H 2 0. 

Dilute. 
4Zn + IOHNO3 = 4Zn(N0 3 ) 2 + N2O + 5H 2 0. 

Stronger. 
3Zn + 8HNO3 = 3Zn(N0 8 ) 2 + 2NO + 4H 2 0. 

Concentrated. 

When zinc is treated with hot sulphuric acid the following 
reaction takes place : 

Zn 4- 2H2SO4 = ZnS0 4 + SO2 + 2H 2 0. 

Alloys. — Mercury forms with zinc an exceedingly brittle 
amalgam. The two combine in the cold state, but union is 
greatly facilitated by heating. 

Silver. — Zinc is said to form two compounds, Ag 2 Zn 3 and 
AgZn with silver. One per cent, of zinc is often added to 
silver to prevent oxidation and to avoid the so-called spitting 
during crystallization. Aluminum and zinc are miscible in 
all proportions but no chemical compounds are formed. 

Platinum. — Combination between zinc and platinum or 
palladium may be effected at a comparatively low tempera- 
ture and is accompanied by evolution of light and heat. 

Zinc and Lead. — These metals are insoluble in one another 
and it requires a high temperature to cause them to be 
miscible at all. If the two metals are melted together and 
allowed to cool they will separate into two distinct layers, 
the zinc having the lesser specific gravity will be the top 
layer and the lead the lower portion. The zinc retains 1.2 



250 ZINC 

per cent, of lead, and the lead 1.6 per cent, of the zinc. The 
necessity of carefully keeping these two metals separate in 
all molding operations in the dental laboratory will readily 
be appreciated, as a failure to preserve precaution in this 
direction will be followed by vexatious consequences. If by 
accident lead becomes mixed with zinc used for dies, the 
lead, by its greater specific gravity, will settle to the bottom 
and fill up the deeper portions of the sand matrix representing 
the alveolar ridge, the most prominent part of the die. This 
may not be discovered until an attempt to swage is made, 
when the die will be found to be totally unfit for the purpose. 
In such cases the mixed metal should be discarded and new 
zinc substituted. 

Zinc and Tin. — These are miscible in all proportions in the 
fluid state but they form no true chemical compound. There 
is a eutectic having 16 per cent, by weight of zinc and 84 per 
cent, tin which melts at 190° C. 

Alloys of zinc and tin are frequently employed in casting 
dies for swaging plates. Richardson's formula consists of 
zinc four parts, tin one part, which he claims fuses at a 
lower temperature, contracts less on cooling, and has less 
surface hardness than zinc. 

Zinc and Copper. — Copper and zinc are miscible in all 
proportions, Bornemann claims the existence of the compound 
Cu2Zn3; other compounds also are said to be formed corre- 
sponding to the formulas CuZn and CuZn 4 . 

Brass. — Brass composed of zinc, 27 to 37 per cent., and 
copper, 63 to 73 per cent., is used in the manufacture of wire 
and sheet brass. 

Mosaic gold, according to Fischer contains 33.3 to 36.7 
per cent, zinc, and copper 63.3 to 66.7 per cent. This alloy 
is so-called because of its color. 

German silver is an alloy of copper, zinc, and nickel. 

Bell metal contains copper, zinc, and tin. 

Galvanized iron is prepared by coating sheet steel with 
zinc by a dipping process. There is supposed to be an alloy 
formed between the zinc and the iron which prevents the zinc 
from separating from the iron. The zinc is not readily acted 



COMPOUNDS OF ZINC 251 

upon by the atmosphere and prevents the oxidation of the 
iron. 

Zinc is the metal most commonly employed in the forma- 
tion of dies for swaging plates. Another important applica- 
tion of zinc is in the formation of counter-dies. The die is 
placed in the iron ring when a Baily flask is employed, or in- 
vested in the molding sand and then surrounded by a suit- 
able iron ring in the old-fashioned way. The zinc is then 
heated and poured in upon the zinc die just at the moment 
of complete fusion. Should the metal be accidently allowed 
to remain on the fire too long, and thus reach a higher 
temperature than is necessary, it should not be poured until 
it begins to solidify at the edges. The belief seems to be 
pretty general that melted zinc cannot be poured upon a 
zinc die without causing cohesion, but if the necessary pre- 
caution regarding the proper temperature at which the metal 
is poured is observed it is impossible for union to take place ; 
when cool the die and counter-die will separate quite as 
readily as though the latter was of lead. It frequently occurs 
that the zinc die and lead counter-die are totally inadequate 
to bring a plate (particularly if the latter is of platinum-gold 
or iridium-platinum) into perfect adaptation to all parts of 
a model, especially where the palatal arch is very deep and 
the rugae are prominent. 

The suggestion has been made of coating the zinc with 
whiting and alcohol mixture in case there is doubt in the 
operator's mind of the advisability of the above procedure. 
Zinc counter-dies are not expected to supersede lead counter- 
dies but to be used in conjunction with them. 

Zinc dies or counter-dies should be handled very carefully 
after pouring. If the die should be dropped while still hot 
its destruction would result. Zinc will, under favorable 
conditions unite with iron, and it frequently attacks the 
cast-iron ladle in which it is melted, and may penetrate the 
side and escape into the fire. Accidents of this kind may be 
prevented by coating the inside of the ladle with whiting. 

Compounds of Zinc. — Zinc oxide is formed when zinc is 
burned in air, it may also be prepared by igniting in air, 
either the hydroxide, carbonate, nitrate, or oxalate. 



252 ZINC 

Zinc oxide for dental purposes should be of a high grade of 
purity. The presence of arsenic in this compound has given 
a great amount of trouble in the past in certain dental 
preparations. Zinc oxide free from arsenic should be pre- 
pared from metallic zinc obtained from ore free from arsenic, 
as arsenic is extremely difficult to separate from zinc and its 
compounds. 

Among the impurities found in commercial zinc oxide may 
be enumerated the following: arsenic, sulphates, chlorides, 
nitrates, and the carbonates of calcium, magnesium and 
foreign metals. 

To test zinc oxide for arsenic the following may be used: 
A mixture of 1 gram of zinc oxide and 3 c.c. of stannous 
chloride solution should not acquire a darker color on stand- 
ing one hour. (Indicating less than 0.0015 per cent, arsenic.) 

Zinc oxide is used in the preparation of dental rubber for 
vulcanite purposes; in the preparation of temporary stopping, 
and finally in dental cements. Zinc oxide is a pure white 
substance which, when heated, turns yellow but again 
becomes white on cooling; when strongly heated in oxygen 
it may be obtained in the form of hexagonal crystals; such 
crystals are occasionally found in the cooler parts of zinc 
furnaces. The oxide does not fuse in the oxyhydrogen 
flame, but like lime, under these circumstances it becomes 
intensely incandescent. 

Dental Cements. — Oxychloride cements consists of a liquid 
prepared by dissolving zinc chloride in water and a powder 
of zinc oxide. 

Oxy phosphate. — The liquid consists of orthophosphoric 
acid, H3PO4, modified with some suitable phosphate. The 
so-called hydraulic cements, i. e., those which possess the 
property of setting in the presence of moisture, generally 
contain a phosphate of a metal other than the alkali metals, 
such as zinc phosphate or aluminum phosphate. The non- 
hydraulic cement liquids contain sodium or other alkali 
metals as a modifying agent. The powder is calcined zinc 
oxide together with coloring agents. There are a few cements 
on the market in which the powder contains phosphates; as 



DENTAL CEMENTS 253 

a rule these are rather slow-setting cements. The other 
dental cements should be described in dental chemistry and 
have no place in metallurgy. The preparation of a dental 
cement is a very exacting procedure, and demands the 
knowledge of a specialist in this branch of chemistry. It 
would be a loss of time, and the writer can see no reason why 
a dentist should be called upon to prepare his own cements; 
for this reason I have not given formulas or exact procedures 
used for the preparation of cements. 

Zinc chloride is prepared by the action of hydrochloric 
acid upon zinc, or by the direct action of chlorine upon 
metallic zinc. It is a soft, white, easily fusible solid which 
volatilizes and distils without decomposition. It is extremely 
deliquescent (absorbs moisture from the atmosphere) . From 
aqueous (watery) solutions, deliquescent crystals are 
deposited, having the composition ZnCl 2 ,H 2 0. 

Besides, as a medicinal agent zinc chloride is also used as a 
flux in soft soldering. In soldering tinware the surfaces 
are coated with "cracked muriatic acid," hydrochloric acid 
in which some zinc has been dissolved. For galvanized iron- 
ware hydrochloric acid alone is used; this acid dissolves 
enough zinc from the metallic surface to form zinc chloride 
which then acts as a flux. 

Resume. 

Symbol, Zn. Chief ore, carbonate, cala- 

Valency,- II. mine. 

Atomic weight, 65.37. Conductivity of electricity, 

Melting point, 415° C. 27.72. 

Specific heat, 0.095. Conductivity of heat, 190. 

Boiling point, 916° C. Coefficient of expansion, 

Malleability, 8th. 0.0000294+ . 

Specific gravity, 6.86 to 7.2. Ductility, 6th. 

Crystalline form, rhombo- Tenacity, 6th. 
hedral. 



CHAPTER XXI. 
NICKEL. 

Symbol, Ni. Atomic weight, 58.68. 

Occurrence. — Garnierite, a magnesium, nickel silicate is the 
principal working ore of nickel, H 2 (NiMg)Si0 4 .H 2 0. The 
other minerals are the sulphides, NiS, millerite and pent- 
landite, (Fe,Ni)S, arsenide, NiAs, niccolite. Nickel is also 
obtained as the oxide in the working of pyrrhotite, Fe 6 S 7 
(sometimes called magnetic pyrites), and chalcopyrite, 
CuFeS 2 , of Sudbury, Canada. 

Native nickel is found with iron in meteorites. 

Reduction. — The oxide may be reduced by the "Mond" 
process. Carbon monoxide is passed over gently heated 
nickel oxide which is first reduced to metallic nickel and then 
the excess of carbon monoxide combines with the nickel, 
forming volatile nickel carbonyl, Ni(CO) 4 . This compound 
is passed through tubes more strongly heated which decom- 
pose it with the liberation of metallic nickel. In this way 
the metal is deposited in a coherent mass entirely free from 
cobalt. 

The sulphide ores are reduced by roasting and then 
smelting with a suitable flux, a nickel matte results which 
contains iron and copper as impurities, this is run into a 
silica-lined Bessemer converter and air-blown. A matte, 
rich in nickel and copper, results. This matte is fused with 
sodium sulphate and coke. The nickel sulphide is roasted 
and converted to the oxide. Then upon heating with char- 
coal to a white heat in a graphite crucible, nickel results. 
Another process of treating the sulphide briefly described is 
as follows: Roasting the sulphide, smelting with a suitable 
flux in a blast furnace forming a matte ; air-blowing the 
fused matte; again roasting which results in the production 



PROPERTIES 255 

of NiO and CuO. Dissolve the oxides in sulphuric acid; the 
copper precipitated .by electrolysis; crystallize nickel sulphate 
from the solution; obtaining the nickel as NiO by adding 
milk of lime and drying the precipitate formed. The nickel 
oxide is reduced by making a mixture of starch and charcoal 
with the oxide into a paste, forming into cubes and then 
heating to a white heat in a crucible. 

There is also an electrolytic method of reduction, the 
details of which are a secret. 

Properties. — Nickel is a hard white metal having a yellowish 
tinge by which it may be distinguished from silver. It takes 
a high polish and is malleable, ductile and very tenacious. 
In wire form it is stronger than iron but not as strong as 
cobalt. It is magnetic but loses its magnetism, like steel, 
when heated to redness. It imparts hardness to its alloys. 

It has always been the belief that the primitive people 
possessed the knowledge of tempering copper; the following 
item, taken from The Engineering and Mining Journal, 
tends to disprove this statement and also shows the effect 
that nickel produces on other metals. The copper-cutting 
instruments of the Tarascans are so hard that they would 
turn the edge of a modern knife, and it has been claimed, 
that these people along with the Aztecs and Toltecs, possessed 
the secret of tempering copper. On the other hand, copper 
knives and axes found at Alcopotzalco are so soft that they 
can be cut with a knife. Analysis shows that in all three 
localities the copper implements were of the same composition 
as the copper ore found therein. 

The blades from Guerrero, which are hard and apparently 
tempered, were made from the natural ore carrying nickel 
and cobalt, thus rendering the smelted alloy steel-like in 
hardness. Thus the natural product gave an alloy of great 
hardness when heated and sharpened, while the other ores 
of practically pure copper, when smelted in implements 
were soft and inferior in cutting value. The sharp-cutting 
implements were therefore the result of Nature's handiwork, 
and it is indeed very questionable whether these people 
possessed the secret of "tempering." 



256 NICKEL 

Nickel is not acted upon in dry air or moist air at ordinary 
temperatures for this reason it is used to coat other metals, 
such as copper, brass, steel, etc., to prevent corroding and 
to preserve a bright metallic surface. The coating is given 
the metals by an electrolytic process. When nickel is heated 
it burns with incandescence in the presence of oxygen, 
chlorine, bromine or sulphur. 

It is possible to weld sheet nickel upon iron and steel; 
advantage is taken of this in the manufacture of " armor 
plate." 

Nickel as coinage possesses three advantages which 
recommends it for the construction of coins of small value : 

(1) It requires enormous pressure to stamp out the coin. 

(2) Resists wear because of its being such a hard metal. (3) 
The commercial value of it is such that a much smaller-sized 
coin may be made from it than of copper and represent a 
greater value. 

Arsenic, phosphorus, aluminum and magnesium con- 
siderably decrease the fusing point of nickel and do not 
interfere with its malleability except when present in excessive 
amounts. 

Solubilities. — Hydrochloric and sulphuric acids, both dilute 
and concentrated, attack nickel but very slowly. Diluted 
nitric acid readily attacks it but concentrated nitric acid 
seems to render nickel passive. It is not attacked by 
alkali hydroxide or carbonates even when fused with them. 

Compounds. — Nickel forms oxides corresponding to the 
formulas NiO, Ni 2 03, and Ni 3 4 . The first is the only basic 
oxide. Nickel sulphate, NiS0 4 ,7H 2 0, is prepared by dissolving 
the oxide in sulphuric acid. This salt is used in electro- 
plating of nickel. 

Alloys. — Copper and nickel alloy, and this alloy is used as 
coinage for coins of small denomination; Belgium, Germany 
and United States coins consist of about 35 per cent, nickel 
and 65 per cent, copper. 

Copper, nickel and zinc form German silver. German 
silver is used in the construction of orthodontic appliances 
and contains about 18 per cent, nickel; objection has been 



ALLOYS 257 

raised to the use of this material because of it deteriorating 
in the fluid of the mouth. For further information upon this 
subject see Items of Interest, 1909. 

German silver wire loses its elasticity upon heating and its 
rigidity can only be restored by working the metal. 

Nickel is also used in some of the substitutes for platinum. 

Resume. 

Symbol, Ni. Chief ore, garnierite. 

Valency, II, III. Conductivity of heat, 12.77. 

Atomic weight, 58.68. Coefficient of expansion, 

Melting point, 1450° C. 0.000016. 

Specific heat, 0.1092. Ductility, 9th. 

Malleability, 10th. Conductivity, of electricity, 

Color, white. 12.94. 

Specific gravity, 8.8. Tenacity, greater than iron. 



17 



CHAPTER XXII. 

TANTALUM. TUNGSTEN. 

These metals are classed as rare elements. Within the 
last few years tantalum has been introduced into dentistry 
for the construction of instruments as, for instance, spatulus 
for working silicate cements, and also instruments used in 
the application of drugs. 

TANTALUM. 

Occurrence. — Tantalum occurs widely distributed in nature. 
It is generally found combined as an acid oxide with other 
metals forming tantalates. The tantalates are usually 
associated with the columbites. The minerals, as a rule, are 
very complex in their composition, frequently containing 
manganese, iron, tin, calcium and several rare metals as 
tantalites or mixed tantalites and columbites. 

Furgusonite, columbite, yettrotantalite and samorskite 
are some of these minerals. 

Reduction. — The oxide Ta 2 5 is extracted from the ores. 
This oxide is readily soluble in hydrofluoric acid. The 
oxide is converted into potassium tantalofluoride, K 2 TaF 7 . 
When this salt is reduced a grayish-black metallic tantalum 
is obtained. The amorphous tantalum is then placed in an 
electric vacuum furnace and submitted to a very high tem- 
perature. From this process a very pure form of tantalum 
is obtained. 

Properties. — The following properties were determined by 
Siemens and Halske: Melting point about 2770° C; atomic 



TANTALUM 259 

weight, 181.8; specific gravity, 16.6; coefficient of linear 
expansion, 0.0000079. 

Tantalum is a very ductile and flexible metal and possesses 
a high tensile strength. It is about the same hardness as 
medium hard steel and is not magnetic; when heated in air 
its surface becomes covered with a yellow oxide and at 400° C. 
this changes to a blue color; at 600° C. it is grayish black 
and upon heating still higher it becomes completely oxidized. 

Tantalum at a temperature sufficient to cause it to glow 
occludes hydrogen, nitrogen and other gases. When heated 
in chlorine it is converted into the chloride. 

Tantalum pentoxide, Ta 2 5 , is formed when the metal is 
heated in air or oxygen. When this compound is fused with 
fixed alkalies an alkali tantalate is formed. There is another 
oxide having the formula Ta0 2 . 

Tantalum chloride, TaCl 5 , formed when the metal is heated 
in chlorine gas, is a volatile yellow solid. Melting at 211.3° 
and boiling at 241.6°. When the chloride is treated with 
water it decomposes, forming the hydrated acid, 2HTa0 3 ,- 
H 2 0,(H 4 Ta 2 7 ). 

Solubilities. — Nitric, hydrochloric, sulphuric acids or aqua 
regia are without action upon this metal. Hydrofluoric acid 
attacks the metal with the formation of the fluoride TaFg. 

Solutions of the alkali hydroxides are without action, but 
when fused with the solid alkalies, alkali tantalates are 
formed. 

Uses. — Tantalum instruments are very resistant to the 
action of corrosive agents. They may be sterilized by boiling 
with acid solutions, or may be heated to a low red heat. 
Iodine, phenol, sulphuric acid and cement liquids, which 
includes the most corrosive of agents used in dentistry, are 
without action upon this metal, consequently brooches and 
cement spatulas may be constructed of this metal. The 
following instruments have been placed upon the market 
made of tantalum: cement spatulas, brooches, burnishers, 
and in fact it is being tried out in almost all forms of instru- 
ments in which its properties recommend it. 



260 TANTAL UM—T UN GST EN 



TUNGSTEN. 

Symbol, -W. (wolfram). 

Until within the last few years tungsten could not be 
produced in the degree of purity in which the metal possessed 
the properties of malleability and ductility. The electrical 
companies had obtained this metal in a brittle form and found 
that it could increase the lighting power of the older filaments 
used in incandescent globes and also at the same time con- 
serve electrical energy. The statement has been made that a 
tungsten globe with the same candle power as the older 
(carbon) filament could be operated at a saving of 75 per cent, 
of electrical energy. The great drawback, however, was that 
the tungsten filament was exceedingly brittle and could not 
be subjected to jars or other disturbances which would tend 
to break the filament. 

Within recent years malleable and ductile tungsten has 
been obtained. A study of its properties has led to the dental 
profession taking up this metal and attempting to adopt it 
to overcome some of the difficulties existing. 

Dr. Price and F. A. Fahrenwald, in reports of the Research 
Department of the National Dental Association, have been 
conducting experiments upon this metal. 

Occurrence. — Tungsten occurs in nature as the acid oxide 
combined with certain metals: Scheelite, CaW0 4 — in this 
mineral the tungsten is sometimes replaced by molybdenum ; 
Wolframite, FeMnW0 4 . These minerals have been used in 
the past for making tungsten steel and also sodium tungstate 
which is used in rendering f abri cs non-inflammable. 

Reduction. — The ore is first concentrated and then receives 
a chemical treatment to produce tungstic acid. 

Reduction from Wolframite. — The ore is first dressed and 
then treated with aqua regia or alkaline carbonates or 
alkaline acid sulphates. The following is the method used 
with sodium carbonate: The wolframite is heated in a 
reverberatory furnace with sodium carbonate; after fusing 
the mass is broken up and digested with boiling water. The 



TUNGSTEN 261 

tungsten dissolves together with silicic and phosphoric acids 
as a silicotungstate and phosphotungstate of sodium. 
Hydrochloric acid is then added to the boiling solution and a 
series of chemical changes take place, resulting in the forma- 
tion of tungstic acid. There are various other processes 
made use of in producing tungstic acid. Metallic tungsten 
may be obtained from tungstic acid by a variety of methods : 

1. By reduction of tungstic acid by hydrogen. 

2. By heating the trioxide with carbon in an electric 
furnace. 

3. By heating to redness a mixture of ammonium tungstate 
or oxide with metallic zinc. 

The tungsten as obtained by these processes is very 
brittle, containing impurities. The following is a condensed 
statement of the methods of preparing ductile and malleable 
tungsten as suggested by the various investigators of this 
subject: The product obtained by the above process is in 
the form of a black or gray powder. In order to render this 
tungsten in a coherent mass, the powdered metal is incor- 
porated with a massing material, and then worked into a 
plastic form. This is then worked into a filament by forcing 
through a die and the filament is then heated to a high tem- 
perature so that nothing but pure tungsten remains. 

The powdered tungsten may be pressed in a mold into 
bar form. The bar is then placed into a furnace and heated 
to 1300° C, hydrogen is passed through the furnace to 
prevent oxidation. It is then further heated in an electrical 
furnace under pressure in an atmosphere of hydrogen. 

Properties. — Wrought tungsten is a bright, steel-colored 
metal, having a melting point between 3000° to 3200° C; 
specific gravity, 19.3. Tungsten is hardened by working 
but not by heating and quenching. The metal may be 
annealed by heating to a white heat. It is non-magnetic, 
very tenacious and ductile. A wire may be drawn toitto 
of an inch in diameter. Its tenacity is several times that of 
steel and its hardness is such that the metal cannot be 
worked on a lathe or by hand. Tungsten is pliable, strong 
and tough, and moist or dry air is without action upon it. 



262 TANTALUM— TUNGSTEN 

Solubilities. — According to W. E. Ruder, wrought tungsten 
is insoluble in hydrochloric, sulphuric and concentrated 
nitric acids. Dilute nitric acid attacks it superficially with 
the formation of the yellow oxide. Aqua regia at ordinary 
temperatures oxidizes the surface of the metal and after 
boiling for four hours only 0.1 per cent, of tungsten was dis- 
solved. The external surface becomes coated with the oxide 
which is not attacked by further additions of aqua regia. 

Hydrofluoric acid does not attack this metal, but a mixture 
of hydrofluoric and nitric acids acts upon it. 

Potassium hydroxide in the fused condition attacks the 
metal. The alkali carbonates when potassium nitrate is 
present and dissolves the metal somewhat. 

Dental Uses. — Tungsten and molybdenum and tungsten 
alloys are at the present time being investigated as a pos- 
sible substitute for platinum. Fahrenwald states: "Ductile 
tungsten and, to a lesser degree, ductile molybdenum meet all 
the specifications of a practical substitute for platinum and 
its alloys. These two defects are its ease of oxidation and 
the difficulty with which it can be soldered. And they may 
have been overcome by coating with a precious metal or 
alloy, the resulting material being in many ways far superior 
to platinum and its alloys." Tungsten has also been sug- 
gested for use as dowels in crown and bridge- work, as a much 
smaller gauge wire may be used, having the same strength 
as a large dowel constructed of some other metal. The wire 
is coated with gold so that it may be soldered. It has been 
suggested that the tungsten pin be coated with casting wax 
and introduced into the root canal. The dowel is then removed 
and gold is cast upon the dowel in the usual manner. Some 
of the tungsten dowels have had brittle spots which has 
caused the fracture of the dowel ; however, there is no question 
but that these spots will be eliminated as the methods of 
producing wrought tungsten is improved upon. 

Several solders for tungsten have been patented within 
the last few years. The description of the patents state 
that tungstates are made use of in the preparation of some 
of these. 



CHAPTER XXIII. 

ALKALI AND ALKALI EARTH METALS. 

The metals included in these groups, their atomic weight, 
symbol, and valencies are as follows: 





Alkali Metals. 












Atomic 




Specific 




Symbol. 


Valency. 


weight. 


Fusing point. 


gravity. 


Sodium 


. Na (Natrium) I 


23.0 


95.6° C. 


0.97 


Potassium 


. K(Kalium) 




39.1 


62.5 


0.875 


Lithium . 


. Li 




6.94 


180.0 


0.59 


Barium 


. . Ba 




137.37 


red heat 


3.75 


Strontium 


. Sr 




87.63 


red heat 


2.4 


Calcium . 


. Ca 




40.07 


760 (vacuo) 


1.58 


Magnesium 


. Mg 




24.32 


750 


1.74 


Beryllium 


. . Be 




9.1 




1.85 






SODIUM. 







Occurrence. — This metal occurs widely distributed in 
nature in combination only. The principal minerals are the 
chloride; halite, NaCl; sulphate mirabilite, Na 2 SO 4 10H 2 O; 
nitrate, NaN0 3 ; carbonate; trona, Na2C03.HNaC0 3 2H 2 0; 
fluoride cryolite, 3NaF.AlF 3 . 

Reduction. — Sodium may be obtained from its compounds : 
(1) By the reduction of the hydroxide with carbon. (2) By 
igniting the hydroxide with iron. (3) By gently heating- 
carbonate with magnesium. (4) By electrolysis of the 
hydroxide. 

Castner's Process. — The sodium hydroxide is run into an 
iron pot and kept in a molten state. The cathode passes 
through the bottom of the pot. The anodes are suspended 
from above. The products of electrolysis are hydrogen, 
oxygen and metallic sodium. The sodium is collected in 



264 ALKALI AND ALKALI EARTH METALS 

perforated ladles which allows the hydroxide to pass back 
into the pots, while the sodium because of its high surface 
tension remains in the ladle. 

Properties. — Sodium is a soft metal which can readily be 
molded between the fingers. It decomposes in air, and 
because of this fact it is preserved under petroleum. When 
placed into water it combines with it, with the liberation of 
hydrogen. 

Upon heating sodium volatilizes as a violet vapor. Sodium 
combines with mercury with violence, forming an amalgam. 
With liquid ammonia, sodium forms a blue solution. 

Compounds. — The compounds of sodium are of more impor- 
tance than the metal, as they are used in metallurgical opera- 
tions. 

Oxides. — Sodium forms two oxides: sodium monoxide, 
Na 2 0, and sodium peroxide, Na 2 02. Sodium monoxide is 
supposed to be formed when sodium burns in nitrous oxide 
at a temperature not above 180°. Sodium peroxide is a 
yellowish-white solid obtained by burning sodium briskly 
in oxygen. This compound is a very powerful oxidizing 
agent and when it comes in contact with organic material 
it frequently causes a rapid rise of temperature inducing 
rapid combustion and the production of a flame. Great care 
should be exercised in using this reagent. 

Some reaction of sodium peroxide may be represented as 
following. 

Na 2 2 + H 2 = 2Na(OH) + O. 

When an acid is present the following reaction occurs : 

Na 2 2 + 2H 2 O = 2NaOH + H 2 2 . 

Sodium hydroxide, Na(OH), is prepared by treating sodium 
carbonate with calcium hydroxide. Sodium chloride, NaCl, 
is found in nature and may be prepared by treating sodium 
hydroxide with hydrochloric acid. When sodium chloride is 
strongly heated it fuses without decomposition. Sodium 
chloride is used to cover crucible charges in metallurgical 
operations, because in the fused condition it prevents the 
oxygen of the air from coming in contact with the crucible 



SODIUM 265 

contents. Sodium chloride is also used to convert certain 
metals into the chloride, for example, copper and silver. 

Sodium carbonate, Na 2 CO 3 .10H 2 O, is prepared commerci- 
ally from the chloride by the LeBlanc or Solvay process. 
When this compound is fused with ores, carbon dioxide is 
given off and the oxide of sodium combines with the impuri- 
ties in the ore, forming fusible compounds, thus acting as a 
flux. It is also used when in the fused condition to wash 
down the sides of the crucible and remove adhering particles. 
It combines with sulphur present in ores or is said to be 
a desulphurizing agent. 

Sodium bicarbonate is prepared by the Solvay process. 
When heated it is converted into the carbonate and reacts 
similarly to that reagent. Sodium borate (sodium tetra- 
borate), Na2B 4 O7l0H 2 O. This is a natural occurring com- 
pound and is a very valuable flux. When heated borax fuses 
to a thin, limpid, liquid mass. 

The salts of boric acid are very hard to volatilize, because of 
this fact they will replace, at a higher temperature, most of 
the other acids from combination. Sulphuric, nitric and 
hydrochloric acids are generally considered much stronger 
and harder to replace from combination with metals than 
boric acid. At an elevated temperature boric acid replaces 
all of these acids from combination. The oxides of the 
metals also combine with the boric acid and form fusible 
salts and as a result the salts of this acid are very useful as a 
flux. Sodium borate is frequently used in this capacity when 
operations are carried on at a temperature of red heat or 
greater. Disodium phosphate, HNa 2 P0 4 ,12H 2 0, is obtained 
by heating phosphoric acid with sodium carbonate. The 
phosphates also form a fusible compound and combine with 
metallic oxide similar to the borates. Microcosmic salt, 
NaNH 4 HP0 4 , on fusing forms NaP0 3 , sodium metaphos- 
phate, and in the presence of metallic oxides combine to form 
double phosphates and pyrophosphates which are fusible. 

Sodium nitrate, NaN0 3 , is found in nature ; it may be pre- 
pared by treating sodium carbonate or hydroxide with nitric 
acid. Sodium nitrate is a white, deliquescent, crystalline 



266 ALKALI AND ALKALI EARTH METALS 

solid. It is a valuable oxidizing agent, and may be used 
to oxidize base metals from alloys of the noble metals. The 
oxide formed is then taken up by the flux thus removing 
contaminations from noble metals. 

POTASSIUM. 

Occurrence. — The metal occurs in nature only in com- 
bination. The principal compounds are : the chloride sylvite, 
KC1; carnallite, KCl,MgCl 2 .6H 2 0; nitrate, KN0 3 . It also 
occurs in many silicates and in the ashes of land plants. 

Reduction. — The metal is obtained: (1) by heating a 
mixture of potassium carbonate and charcoal; (2) by 
electrolysis of the hydroxide or the cyanide. 

Properties. — Potassium is a silver-white metal, very soft 
at ordinary temperature, but becomes brittle at 0°; when 
heated, air being excluded, potassium boils and the vapor 
is emerald green. It reacts with water violently and the heat 
of the reaction is sufficient to cause the hydrogen given off 
to unite with oxygen of the air and a violet flame is produced. 
The metal oxidizes so readily that it must be preserved under 
naphtha. Potassium and sodium form a liquid alloy which 
is sometimes used in dentistry for the treatment of putrescent 
pulps and also to enlarge root canals. Potassium, like sodium, 
forms a great number of very useful salts. Potassium nitrate, 
KN0 3 , and the chlorate, KC10 3 , are used as powerful oxidizing 
agents, the latter salt must be handled with great care, as 
violent explosions have occurred in carelessly handling this 
compound. 

Potassium Cyanide. — The cyanides are for the greater part 
all artificially prepared. They are particularly noted for 
their poisonous properties and for this reason should be 
handled with extreme care. Potassium cyanide is obtained 
from yellow prussiate of potash by heating in the presence 
of a reducing agent (chlorine or potassium carbonate) . It is 
obtained in amorphous blocks of a grayish color. Potassium 
cyanide is readily soluble in water and the solution possesses 
the property of dissolving gold and silver when air is present. 



LITHIUM 267 

Solutions of this salt are also used in electroplating. Potas- 
sium cyanide forms double salts with the cyanides of iron. 
Potassium ferrocyanide, K 4 Fe(CN) 6 , and potassium ferri- 
cyanide, K 6 Fe 2 (CN)i 2 , are used in testing for iron, both 
quantitatively and qualitatively; the former salt is also used 
to some extent in tempering iron. Potassium salts are 
nearly all soluble, the exception to this rule is the compound 
formed with platinic chloride, potassium chlorplatinate, and 
the following: potassium fluosilicate, potassium perchlorate, 
potassium tartrate (slightly soluble). I 

LITHIUM. 

Occurrence. — This metal occurs widely distributed but 
only in small quantities. Traces are found in quite a few 
minerals. It also occurs in small quantities in the vegetable 
kingdom. 

Reduction. — Lithium is obtained from its compounds by 
the electrolysis of the fused chloride. The metal may also 
be obtained by igniting with metallic magnesium. 

Properties. — Lithium is the lightest of known solids, having 
a specific gravity of 0.5936. It does not volatilize at red heat 
and is harder than sodium or potassium but softer than lead. 
Lithium may be drawn into wire or rolled into sheets. It 
does not react so violently as sodium and potassium and must 
be heated to 200° before it will combine with oxygen, it 
then burns, giving off a very intense white light. The salts 
of this metal impart a crimson color to the Bunsen flame. 

Barium, Calcium, and Strontium. — These metals are of very 
little importance from a metallurgical point of view. They 
may be obtained by the electrolysis of their fused chloride. 
Their natural occurring compounds are often associated 
with the minerals of the more useful metals, and the removal 
of these compounds is often a problem which presents itself 
to the metallurgist. Calcium carbonate is often used to aid 
in the removal of silicates and other impurities in an ore of an 
acid nature. 

Calcium sulphate is a natural occurring compound; this 



268 ALKALI AND ALKALI EARTH METALS 

mineral is known as gypsum, CaS0 4 2H 2 0. Upon heating, 
gypsum loses some of its water of crystallization and a 
compound having the formula (CaSO^HO is produced. 
This substance is known as plaster of Paris and possesses 
the property of again taking up moisture and setting to a 
hard mass through a process of crystallization. 

Plaster of Paris is used, in conjunction with other materials, 
to form a refractory substance. 

Calcium oxide, CaO, possesses great resistance to the 
action of heat. In the oxyhydrogen flame it glows and gives 
off an intense white light. Blocks made of this substance 
are used in melting platinum and other metals possessing 
high fusing points. Calcium carbonate, CaC0 3 , is used as a 
basic flux in the iron industry, it loses carbon dioxide and 
is converted into the oxide. 

MAGNESIUM. 

Occurrence. — Magnesium occurs as the sulphate, carbonate, 
and hydroxide. It is never found in the free state. 

Reduction. — The metal may be obtained by the following 
process: (1) By the electrolysis of the chloride or sulphate. 
(2) By ignition of the chloride with metallic sodium or 
potassium. 

Properties. — Magnesium is a white, hard, malleable and 
ductile metal, not acted upon by water or alkalies at ordinary 
temperature. When heated in air or oxygen it burns with 
incandescence to form the oxide MgO. When heated it 
combines directly with nitrogen, phosphorus, arsenic, sulphur, 
and chlorine. Metallic magnesium possesses the property of 
liberating the metals from combination and it may be used 
in the same capacity as aluminum (Goldschmidt process, 
thermite) ; however, metallic aluminum will liberate metallic 
magnesium from its compounds. It forms alloys with 
mercury and tin which decompose water. 

Alloys of aluminum and magnesium are said to possess a 
very low specific gravity and also have an exceedingly high 
tensile strength. 



BERYLLIUM 269 

Magnesium oxide, MgO, is a white infusible powder 
frequently used to line metallurgical furnaces. When this 
compound is mixed with a solution of magnesium chloride, 
MgCl 2 , the mass possesses the property of setting, forming a 
very dense substance. 

BERYLLIUM. 

Beryllium is a rare metal occurring as the silicate phenakite, 
Be 2 Si0 4 , and in some other silicates. The metal is a white, 
malleable substance and is not acted upon by air at ordinary 
temperatures. It does not decompose water or steam even 
when heated to a red heat. Oxygen or sulphur scarcely 
attack it. The metal is soluble in acids except when in 
compact form, when nitric acid is without action upon it. 
Salts of this metal are claimed to be used in certain dental 
cements. 



CHAPTER XXIV. 
AMALGAMS. 

An amalgam may be defined as an alloy of two or more 
metals, one of them being mercury. The same law holds 
true for amalgams as for alloys in that they may be chemical 
compounds, mixed crystals, eutectics, or mixtures of all the 
above. 

Mercury is a very peculiar metal, having the lowest fusing 
point of any metallic substance, and as this temperature is 
far below that of ordinary atmospheric conditions, it is 
rendered a liquid. When mercury is mixed with other metals 
it reduces their fusing point in a remarkable manner. Com- 
paring the alloys of mercury with that of some other metals 
it will help to explain the phenomenon of amalgamation to 
a certain extent. Consider an alloy of lead, for example. 
When lead and higher fusing metals are alloyed, chemical 
compounds, etc., may be formed. It is possible to have the 
lead present in such excess that it will only carry minute 
quantities of some metal for which it has an affinity; now, 
if the lead solidified at the ordinary temperature of the 
atmosphere it would be possible to express the surplus 
quantity which is present and the resultant alloy remaining 
would then slowly congeal. On the other hand, if the sur- 
rounding temperature be kept to that at which lead fuses 
the same phenomenon will take place, that is, the surplus 
lead may be expressed. 

When mercury is mixed with another metal it is possible 
to have the three conditions present (chemical compound 
formed, etc.), the surplus mercury may be expressed or, 
comparing with the lead analogy, the mass might be cooled 
to the fusing point of mercury and the entire mass would 
then solidify. With most amalgams we are working at the 



BEHAVIOR OF MERCURY TOWARD METALS 271 

temperature above the melting point of mercury and to 
remove this excess quantity pressure is used, thus leaving 
the metallic mass having the highest fusing point, then 
crystallization takes place and solidification results. 

Setting of Dental Amalgams. — As in other alloys so with 
amalgams (the mercury when added to a mixture of metals 
or an alloy), there may be a greater adhesive force between 
the mercury and some particular metal and this force may 
be greater than the force of cohesion; in this case amalgama- 
tion readily takes place between the metals and mercury 
even at the exclusion of the other metals present. 

Silver and mercury combine and form a chemical com- 
pound, and in the presence of a slight excess of mercury this 
compound combines with another portion of mercury, and 
when rubbed in the palm of the hand a gritting sound is given 
off, indicating that the mass is crystalline. The theory has 
been advanced that the same phenomenon takes place in the 
setting of an amalgam alloy, i. e., that the crystals of amalgam 
first formed dissolve in a slight excess of mercury and then a 
new crystalline growth takes place causing the setting of the 
amalgam. Even after this takes place, there is no question 
but what future changes take place in an amalgam, and any 
factor which would tend to disturb the equilibrium existing 
after the primary setting will cause changes in the amalgam 
mass. 

Behavior of Mercury toward Metals. — Direct Combination. 
— 1. Mercury combines with some metals directly; in some 
cases there is every evidence of a chemical compound being 
formed. Sodium and potassium when heated to 440° com- 
bine with mercury with the formation of crystalline com- 
pounds having the formula Na 3 Hg and K 2 Hg. When com- 
bining there is frequently a violent reaction indicating 
chemical union. Mercury may combine readily with a 
metal without giving any perceptible evidence of a chemical 
change, but upon examination there may be found that com- 
pounds are formed. With tin the union is without any 
perceptible evidence of a chemical change, but, nevertheless, 
chemical compounds are formed. 



272 AMALGAMS 

2. Some metals only unite with mercury when they are 
in a finely divided condition. In fact most metals combine 
with mercury much more readily when in the finely divided 
state. To obtain the metal in this condition a soluble salt 
of the metal is used and a strip of a more electropositive 
metal is then placed in the solution; this causes the first metal 
to be thrown down in a finely divided condition. To illus- 
trate, iron when placed in a solution of copper sulphate; 
zinc will have a similar effect upon silver solutions. 

3. Amalgamation by Indirect Means. — Mercury will not 
unite directly with some metals, under these conditions 
amalgamation may be produced by treating the metal with 
a salt of mercury. In other cases a salt of the metal is treated 
with mercury. Mercury in the form of vapor combines with 
metals; if gold leaf be placed in the neck of a bottle containing 
mercury, even at ordinary temperatures, the vapor arising 
from the surface of the mercury will cause the whitening of 
the surface of the gold, showing that amalgamation has taken 
place even under these conditions. 

Amalgams are sometimes named according to the number 
of metals they contain. 

Binary amalgams contain one metal with mercury. 

Ternary, quaternary, quinary having respectively two, 
three or four metals with mercury. 

The simpler forms of amalgams are used for commercial 
purposes; tin amalgam in the construction of the cheaper 
forms of mirrors, gold is amalgamated and the mercury is 
then boiled off, giving the gold surface a characteristic 
appearance. Zinc amalgam is used to coat zinc poles of wet 
cells to prevent polarization. Through the formation of the 
amalgam silver and gold are separated from other metals 
and impurities in the recovery of these metals from their ores. 

The more complex amalgams are used in dentistry as a 
filling material. An amalgam must possess certain require- 
ments in order to be suitable for a filling material; among 
these the following may be enumerated: 

1. After introducing into cavity it should possess per- 
manency of form and absolute resistance to chemical 
substance. 



MANIPULATION AND WORKING PROPERTIES 273 

2. Its color should not be objectionable. 

3. It should possess good working qualities and be easily 
manipulated. 

Permanency of Form. — Under permanency of form there 
are two phenomena to be considered: 

1. Changes due to a lack of proper physical properties 
possessed by the amalgam. 

2. Changes due to a lack of chemical resistance upon the 
part of the amalgam. 

During the process of solidification an amalgam should 
not contract, for in so doing a faulty joint will be produced 
which will leave the tooth in such a condition that the factors 
which produce caries may again attack the tooth substance, 
causing recurrent decay, and the tooth will in no way 
be benefited by such a filling. Expansion to a very slight 
degree is permissible. However, expansion beyond this very 
limited degree will also cause faulty margins and leakage of 
the filling material will result. It should possess sufficient 
hardness to withstand the force of mastication and sufficient 
strength to retain its margins. Under stress amalgams possess 
the property of solid flow to a greater or less extent, this 
property should not be present in an appreciable amount, 
neither should the amalgam assume the spherical form; 
both of the factors tend to decrease the permanency of an 
amalgam filling. 

Chemical agents in the mouth may attack an amalgam, 
forming salts which would cause a discoloration of tooth 
substance and also the fillings; in some cases these salts 
may be injurious to the general health of the patient. The 
amalgam should not possess too great a potential difference 
from that possessed by other filling materials used. 

Color. — At the best, the color of amalgam can hardly be 
said to be unobjectionable; however, some amalgams are 
more unsightly than others. 

Manipulation and Working Properties. — To the author this 
is one of the most important phases of this subject. Using 
an e very-day expression, an amalgam should be "fool-proof." 

There are a great many factors that influence the per- 
18 



274 AMALGAMS 

manency of form of the amalgam filling; with the products 
as prepared by the better manufacturers of this article there 
is little room for doubt but that the poor showing of some 
amalgam fillings is, in great part, due to a lack of proper 
technic in incorporating mercury with the alloy. I have 
observed various operators manipulating amalgams and have 
found that, at best, this operation is carried out in a hap- 
hazard manner. If we were as careless in our manipulation 
of gold as we are with amalgams, gold certainly would have 
been considered years ago as a material totally unfit for 
filling purposes. 

The working properties of an amalgam should be such that 
the proper contour may be given to the filling so that the 
lost parts of the tooth structure cannot only be reproduced 
but also correction of the deficiencies existing. 

Discoloration. — The metals used in dental amalgams are 
attacked by hydrogen sulphide, which is present in the mouth 
to a greater or less extent. Both silver and mercury combine 
with this agent, forming black sulphides. If an alloy filling 
be placed so that it comes in contact with gold, the amalgam 
will be discolored; in this case the discoloration is due to 
electrolysis. 

Tooth substance is also attacked by the metallic salts 
formed and upon examination it will be found that the con- 
tents of the dentinal tubule is colored black. This coloration 
may be due in part to the formation of sulphides and also to 
the effect of silver salts acting upon the albuminous materials 
present in the tubule. Leaky fillings will cause the retention 
of food material which undergo decomposition and the 
products formed attack the alloy with the production of 
metallic salts, these in turn will discolor the tooth. Noble 
metals when added to amalgam do not increase their resist- 
ance to such agencies. 

Dental Amalgam Alloys. — A dental amalgam alloy is an 
alloy intended to be incorporated with mercury, to form 
an amalgam which is used as a filling material in dental 
operations. 



EDGE STRENGTH 275 

These alloys may contain the following metals: silver, 
tin, copper and sometimes zinc, gold or platinum. 

Certain terms are used in the study of amalgams. Their 
description follows : 

Flow. — Amalgams are, as a rule, brittle bodies, and when 
pressure is applied in sufficient quantity fracture will result; 
however, under a more moderate pressure over a longer 
period of time amalgams may change their form. Dr. 
Black, in speaking of this phenomenon, states that amalgams 
are brittle, but are exceptions to the general rule in that they 
are also somewhat malleable. Flow then may be defined 
as the change in form of an amalgam under slow-continued 
pressure. Some amalgams seem to change their forms and 
attempt to assume a spherical shape. Liquids if unacted 
upon by external forces, tend to assume the spherical shape, 
as this geometrical form has the least surface for a given 
volume. In this case spheroiding is due to gravity. 

Spheroiding. — Spheroiding is the term used to designate 
the property of an amalgam of attempting to assume the 
spherical form. Attempts have been made to explain the 
spheroiding of amalgams according to the same phenomenon 
as occurs in liquids. 

Edge Strength. — Some amalgams are so brittle that they 
will not retain a fine edge and during the process of masti- 
cation this surface is fractured away and thus produces a 
faulty filling. Edge strength may be defined as that strength 
possessed by an amalgam to resist rupture at its margins. 
Some amalgams cannot be manipulated so as to retain a 
very fine margin. In this attenuated condition some are so 
brittle that they cannot withstand the force of mastication, 
in others the amalgam will form a rounded edge and this also 
is an objection. If proper regard has been taken as to 
cavity preparation, very little fear may be felt from this 
source in the better grades of alloys. In alloy fillings which 
have been in situ for some time it may be frequently observed 
that the margins are very irregular. This irregularity may 
be due to some of the causes already mentioned, i. e.\ (1) 
Contraction of the alloy after inserting. (2) Slow changes 



276 AMALGAMS 

occurring after the first setting. (3) Lack of edge-strength. 
(4) Finally, the effect of the alloy upon the interprismatic 
substance of the enamel. The enamel at these margins is 
exceedingly brittle and it shows stain from the amalgam, 
and it is very evident that this factor has something to do 
with the faulty condition sometimes existing about the 
margins of old amalgam fillings. 

As has already been stated, if the margins have received 
their proper bevel this trouble may be reduced to a minimum. 

Aging. — Aging is simply a process of annealing a dental 
amalgam alloy. This process consists of uniformly heating 
the alloy to a certain temperature for a given length of time. 
It was at one time thought that by this operation the particles 
of the alloy were superficially oxidized; however, Dr. Black 
has proved that the heating simply causes an adjustment of 
the molecules of the alloy to their normal relations. As a 
result of the rapid cooling of the ingot and also the mechanical 
procedure used in reducing the alloy, a strained condition 
of the molecules exists. Just the same as in the case of 
annealing a piece of gold the normal arrangement of the 
molecules is brought about by heating, so in the case of 
these alloys. The aging of alloys, however, is a very par- 
ticular process ; the time and temperature are governed by the 
physical properties of the metals present in the alloy. The 
new mix of metals must be tested before the proper aging 
can be determined ; from this we see that no set temperature 
or time may be stated. 

If aging is carried too far it affects the working property 
of the amalgam, causing slow setting, and the alloy requires a 
smaller quantity of mercury to amalgamate and finally it 
may completely overcome the slight expansion and even 
cause the alloy to contract. Aging may be accomplished 
by heating to a higher temperature for a short time, but the 
results accomplished are not so uniform. Dental amalgam 
alloys age even at ordinary temperatures, and this may 
affect the properties of the alloy to such an extent as to com- 
pletely change its physical properties and render same useless 
as a filling material. An alloy that is not aged by the manu- 



BALANCED ALLOY 277 

facture would undergo a slow process of annealing upon 
standing and its properties would thus change from time to 
time and the product would not be one that could be depended 
upon. All that may be expected from this process is to 
overcome to a great extent those changes which would occur 
in the alloy as the result of heat and the time elapsing 
between the comminution and the inserting of the alloy as a 
filling material. Even alloys that have been aged should not 
be kept in stock for any length of time, as the aging which it 
receives may render its properties entirely different from 
those tested out by the manufacturer. 

It is very good practice for the dentist not to purchase 
this material in too large quantities, but rather to replace 
his stock at shorter intervals of time. 

Balanced Alloy. — A balanced alloy is one in which the 
physical properties of the alloy is so modified that when the 
amalgam prepared from it sets there will be no contraction, 
and in the strict sense of the term the amalgam should 
neither contract nor expand. 

In the construction of a dental amalgam alloy silver is 
the expanding element and tin is the metal favoring con- 
traction. When these two metals are alloyed in certain 
proportions, an attempt is made to have the expansion of 
silver neutralize the contraction of tin. This is not balancing 
an alloy. In order to produce a balanced alloy the metals 
are alloyed and the resultant alloy is tested as to its shrinkage 
or expanding properties; whichever condition exists, this 
amount of shrinkage or expansion is balanced by incorporat- 
ing some other alloy possessing an opposite property. If the 
freshly prepared alloy contracts, then a sufficient quantity 
of an alloy which has been tested and found to expand is 
added, and in this way a balanced action as regards contraction 
and expansion is brought about. As aging favors contrac- 
tion, and as a slight amount of expansion tends to insure a 
perfect joint between the amalgam and the cavity wall, 
most balanced alloys are prepared so as to expand slightly. 
The amount of this expansion is exceedingly small and is 
measured in ^Vu" of an inch. 



278 AMALGAMS 

The alloying of metals for the preparation of dental 
amalgam alloy is not as simple as might be supposed. If 
these metals are fused in the ordinary way there is every 
liability of the metals oxidizing, and thus cause an alteration 
in the composition of the alloy. Special precautions must 
be taken in the selection 'of a suitable crucible, as con- 
tamination may be introduced from this source. 

One method of producing this alloy consists of fusing the 
tin in an electric furnace in an inert atmosphere and then 
adding the silver and other constituents. This may be 
accomplished at a comparatively low temperature (dull 
red heat), while if the silver be first fused the temperature 
is so high that there is a probability of not obtaining a 
homogeneous mixture. 

Great care is necessary to produce a homogeneous mixture. 
The writer has made it a practice for the last four or five 
years to have classes make a qualitative test of these alloys, 
and in two cases one-half of the class found copper and the 
other half absolutely could not obtain a test for this metal; 
homogeneity was lacking in these alloys. 

After the metals have fused every precaution, by agitating, 
stirring and gradual cooling, should be used to insure a 
uniform mixture. The alloy is then poured into a suitable 
mold. The ingot is then reduced into filings or shavings, 
by suitable files or lathes. The process of reducing the alloy 
to a suitable form so as to be used is known as comminution. 
The alloy is then treated with a strong magnet to remove any 
steel which may have been introduced from the files. Care 
must be taken as to the condition of the filings or shavings, the 
more nearly uniform they are in size the more uniform will 
be the properties of the amalgam. This condition of the 
prepared alloy has a direct influence upon the quantity of 
mercury used and is indirectly a factor in expansion and 
contraction. The alloy is now ready for the aging process. 
The temperature at which the aging is produced is governed 
by the composition of the alloy and also the length of time 
to which it is subjected to the heating process. 



PROPERTIES OF DENTAL AMALGAM ALLOYS 279 

Testing the Physical Properties of Dental Amalgam Alloys. 
—A sufficient quantity of the alloy is placed in a porcelain 
mortar and about an equal weight of mercury is then added, 
the mass is then triturated until the mercury is thoroughly 
incorporated with the alloy, additional quantities of mercury 
are added until the amalgam possesses sufficient plasticity 
to be worked between the fingers without separating. When 
this degree of amalgamation has been reached the amalgam 
is removed from the mortar and thoroughly kneaded in 
the palm of the hand. The slight excess of mercury is then 




Yig. 59. — The Wedelstaedt steel test-tube, and one steel slide for the 
microscope. 

removed by squeezing the amalgam in a chamois leather. 
The amalgam is then worked into a Wedelstaedt test-tube 
(Fig. 59). In this operation small pledgets of the amalgam 
are introduced at a time and mallet force is used to thor- 
oughly condence the amalgam. The excess mercury separ- 
ating from the amalgam from time to time is removed and 
then additional pledgets of amalgam are added and this 
operation is continued until the test-tube is completely filled. 
The margins are carefully finished and the amalgam allowed 
to set. 



280 



AMALGAMS 



The Wedelstaedt test-tube is simply a steel block having a 
circular concavity of def nite size and milled so as to have 
perfect margins. It is used as a receptacle for the amalgam 
while it is undergoing the hardening or setting process. 
Any changes produced about the margins may be observed 
by the use of the amalgam micrometer. 




Testing for Expansion and Contraction. — The amalgam 
micrometer (Fig. 60) is one gotten up at the suggestion of 
Dr. G. V. Black. The test-tube is placed under the lens 
and the conditions of the margins noted. The circular 
dial is connected with a pointer under the lens, and by the 
turning of the thumb-screw on the left of the platform the 
amount of change in the amalgam is recorded by the gradua- 



CONTRACTION 281 

tions on the dial. This is but one form of micrometer, and 
some of these instruments are so regulated that one point 
on the dial is equal to 40000 of an inch. A point on this 
micrometer would mean a contraction or expansion of ^nrror 
of an inch. Some definite standard should be used as to the 
value of a point in all of the various makes of micrometers; 
the writer is very much in favor of adopting the value of a 
point as having the same value as a micron. In this way a 
comparison may be readily made with the size of the micro- 
organisms, as this is the system of measurement made use of in 
bacteriology. Miller describes the jodococcus vaginatus as 
being 0.73 micron in thickness. Spirillum sputigen is described 
as 0.1 to 0.3 micron in breadth and 1 to 2.5 microns in length. 

The diameter or width of the microorganisms have a 
direct bearing upon the standard to be arrived at as regards 
contraction or expansion of an amalgam. As microorganisms 
are the active factors in the cause of caries, the margins of a 
filling should be such as to exclude these agents to the highest 
degree. Considering the size of the jodococcus as 0.73 micron, 
which would be equivalent to about T 82500 of an inch, 
it becomes evident that an amalgam which contracts to the 
least degree would be absolutely worthless as a filling material. 
In the above case the mathematical calculation becomes 
comparatively easy when a point is equal to 1 micron. 
Taking a point as the value of 1 micron, then the above 
microorganism would of course have a breadth of 0.73 point. 
Dr. Crandall is using an instrument so graduated that a 
point is 2T U"o~o inch. This more nearly approximates the 
value of a micron which has the value of 25399. 5T °f an 
inch or in round numbers -^sr^ °^ an inch. By using the 
point on Dr. Crandall's instrument as equivalent to the 
micron it would introduce an error of only 1.5 parts in a 
thousand; however, it would only be a simple matter to 
change the graduations on all of these micrometers to be 
exactly equal to the micron and then uniformity in measure- 
ment would be established. 

Contraction. — As has already been stated, this property 
should be absolutely lacking in a dental amalgam. As the 



282 



AMALGAMS 



amalgam alloys are now prepared this property is eliminated 
when the product leaves the factory, but the slow process of 
aging which the alloy receives upon standing, due to the 
agencies of heat, is liable to overcome the slight expansion 
originally possessed by the alloy and render the product a 
contracting amalgam. 

Expansion.— A slight amount of expansion is beneficial; 
however, the exact amount can hardly be stated; some of the 
manufacturers claim that it should not exceed 0.6 micron. 
It is the author's opinion that this amount may be greatly 
exceeded even to the extent of 8 or 9 microns. The points 
to be considered in this case are: 




Fig. 61 

1. If the amalgam does not expand sufficiently, it will not 
be permanent enough to withstand a sufficient amount of 
aging, while in the hands of the dental depots or the dentist, 
before using. 

2. An excess of expansion would cause the filling to bulge 
from its margins. 

Flow and Crushing Strength.— Suitable molds of definite 
size are used to obtain cubes of the alloy. Fig. 61 illustrates 
a set of these instruments as gotten up by Dr. G. V. Black. 
The cube is placed in the dynamometer (Fig. 62) and force 
applied by means of the thumb-screw D, the amount of 



FLOW AND CRUSHING STRENGTH 283 




Y 1Q . 62.— The dynamometer. The instrument in position for use. 



284 AMALGAMS 

force applied is recorded upon the dial H; the flow is 
recorded by adjusting the thumb-screw J, and upon reading 
the dial K, the amount of flow may be ascertained. 

According to the experiments made at the Northwestern 
University, the average force of mastication as obtained 
from 1000 cases tested was 171 pounds. Taking this as 
a standard, amalgams should not show any appreciable 
amount of flow when this amount of pressure is applied. 
The result of an excessive flow in an amalgam would be such 
that the permanency of the filling would be impaired, and 
this property may be developed to such an extent as to 
fracture tooth substance. There must be a balance between 
flow and brittleness, as when flow is absolutely lacking 
brittleness is developed to such an extent that the amalgam 
will be low in crushing strength. 

The amalgam should possess sufficient crushing strength 
in order to withstand the forces of mastication. This property 
is constantly subject to change at all times, and the strength 
of an amalgam filling will be found to have considerably 
decreased up to the time of six months after the insertion 
of the filling. This change should be expected to a greater 
or less degree, and to overcome this fault the freshly set 
amalgam should possess sufficient crushing strength, so that 
when this depreciation takes place the amalgam will still 
have sufficient strength to withstand the average 171 pounds 
of force exerted during mastication. 

The method of manipulating the amalgamation has a 
direct effect upon this property. A mixture in which an 
excess of mercury has been used, and the excess not removed, 
will invariably result in a very brittle filling. An excessive 
amount of trituration tends also to weaken the amalgam; 
and still another condition which is of the greatest importance 
is the proper condensation of the amalgam. 

Microscopic tests are also made use of in order to determine 
the crystalline structure and the degree of homogeneity of 
the amalgam. The observations may be made upon a frac- 
tured surface of a specimen of an alloy, or a second method 
may be used in which the surface of the amalgam is etched 
and highly polished and then placed under the microscope. 



MERCURY 285 

Mercury. — In the preparation of dental amalgam alloy 
every precaution is taken to have this product free from 
contaminations, and painstaking tests are made to render 
the physical properties of the amalgam as near perfect as our 
knowledge of the subject will permit. Just as much care is 
necessary in selecting the mercury as in the selection of the 
other metals. The use of ordinary commercial mercury is 
not a wise procedure, as it invariably contains metallic 
impurities which would tend to alter the physical properties 
of the amalgam. 

The quantity of mercury used in amalgamation is also an 
important factor. If too little is used, a crumbly mass is 
produced which does not possess the sufficient amount of 
plasticity to allow the proper condensation necessary in 
introducing the filling. Such an amalgam is low in crushing 
strength. 

When a large excess of mercury is used the composition of 
the alloy may be changed, due to the differences in solubility 
of the various metals making up the dental amalgam alloy. 
Upon squeezing out the excess of mercury tin will be lost 
to the greatest extent, while only a small quantity of silver 
will be carried by the mercury. The quantity of silver which 
may be lost in this way amounts to about 1.12 per cent. 
If the excess of mercury be not expressed at the time of intro- 
ducing the amalgam, it will gradually be lost from the surface 
of the amalgam after setting and leave a brittle alloy having 
irregularities upon its surface. 

A dental amalgam alloy requires the presence of a slight 
excess of mercury during the amalgamation process in order 
to insure a homogeneous amalgamation. The commercial 
products generally state the quantity of mercury which 
they have found by testing, as the correct amount, upon the 
circular enclosed with the alloy. It is best to use some form 
of measuring device in order to determine the quantity 
the operator is using; any other method of procedure is 
absolutely guesswork. 

The object of amalgamation is not to dissolve all of the 
alloy in mercury but simply for the mercury to combine 



286 AMALGAMS 

with the surface of the alloy particles, and this amalgam upon 
setting acts as a cement to join the mass together. As the 
results of this there is actually only a comparatively small 
amount of amalgam setting, and this reduces the changes in 
volume which are produced during the crystallization to a 
minimum. 

The mercury first combines with these surfaces and an 
additional quantity of mercury is gradually taken up; the 
latter product determines the setting property of the 
amalgam. If this additional quantity is taken up rapidly, 
it is generally indicative of a low silver alloy, as tin takes 
up mercury much more rapidly than silver. On the other 
hand, a slow amalgamating and setting alloy may indicate 
a high silver alloy. It must be borne in mind that the above 
is only approximately true, as other conditions may also 
cause this same effect; among these may be mentioned 
the degree of comminution and the aging of the alloy. Most 
of the manufacturers direct that a larger weight of mercury 
be used than alloy; however, after the slight excess of mer- 
cury has been removed by pressure, the alloy is present in 
a very slightly larger proportion than the mercury. 

Properties of Amalgams. — Tin. — Tin combines very readily 
with mercury, forming quite a few chemical compounds. 
With large quantities of mercury a fluid amalgam may be 
obtained. The solid amalgams are said to expand upon 
setting. Tin amalgam does not possess sufficient crushing 
strength to be used as a dental amalgam. It also forms 
rounded margins and pulls away from the walls of a mold. 
However, when alloyed with silver it aids in amalgamation, 
and also tends to overcome the expansion of the silver during 
setting. 

The following are the properties which tin is supposed to 
impart to dental amalgam: it assists in amalgamation, over- 
comes brittleness, increases flow, retards setting, lessens 
edge strength, aids in lightening the color and tends to cause 
contraction. When it is present in excessive amounts it 
renders the amalgam granular. The proportion of tin to 
silver, in which the expansion of the latter would overcome 



PROPERTIES OF AMALGAMS 287 

the contraction of the tin, received a great amount of atten- 
tion from Dr. Black. According to his determinations, 
alloys containing silver up to 64 per cent, contract; at 
65 per cent, the contraction of tin is overcome, and this was 
considered the point at which a balance was obtained. Alloys 
containing more than 65 parts of silver expand. Fenchel 
shows by his experiments that alloys containing from" 57.8 
to 64.47 per cent, silver have the expansion of silver over- 
come by the contraction of tin. An alloy containing 72.5 
silver expands the greatest of all of these alloys. As has 
already been stated in the balanced alloys, all that is expected 
of these metals upon alloying is to approximately balance 
the contraction and expansion, the deficiency is then over- 
come by other prepared alloys. 

Silver. — Silver slowly amalgamates with mercury when in 
the massive form or as shavings; in the finely divided con- 
dition amalgamation takes place more rapidly. In the 
dental amalgam alloy silver ranks next to tin in its affinity 
for mercury. 

According to Dr. Black, 1 a pure silver amalgam upon 
setting contracts for the first twenty-four hours; after this 
period of time has elapsed it remains stationary for from 
twelve to twenty-four hours and then slowly expands. This 
expansion which continues for three or four days finally is 
greater than the shrinkage in alloys containing but 40 
per cent, of silver. 

Silver is said to impart the following properties to a dental 
amalgam: it tends to form salts and causes discoloration 
of tooth substance and also darkens the amalgam; it tends 
to overcome contraction of tin; it increases the crushing 
strength, thus lessening flow. 

Copper. — Copper amalgamates slowly, and in order to 
form an amalgam indirect methods of amalgamation are 
used. The copper is thrown down from the solution of 
the sulphate by metallic iron, and amalgamation is started 
by adding mercuric nitrate solution. After the amalgama- 

1 Dental Cosmos, vol. xxxviii, p. 82. 



288 AMALGAMS 

tion is started, metallic mercury added and heat applied, 
copper amalgam is obtained. This amalgam was at one 
time extensively used as a filling material. The method 
of working differed from that used in the manipulation of 
our present-day amalgams. Copper amalgam was put upon 
the market in lozenge shape and when used was heated in an 
iron spoon; the excess of mercury was then expressed after 
the mass had been triturated. It behaved in a very peculiar 
manner; some fillings would preserve their margins beauti- 
fully, and the tooth substance would show very little, if 
any discoloration; it would not change form under the 
stress of mastication and seemed to possess germicidal 
properties in preserving the tooth from future decay; the 
external surface of the filling quickly became coated with the 
sulphide and turned black; however, this coloration did not 
penetrate the tooth. In other cases it produced poor margins, 
stained the tooth, causing a dark discoloration, showing 
every evidence of a leaky filling and under these conditions 
it appeared absolutely unsuited for filling purposes. The 
copper amalgam required great care in producing good 
margins, but it was the common belief that good margins 
once formed with the material remained in this condition 
and were not subject to changes. Because of this difference 
in behavior of copper amalgam some operators were strong 
in their praise, while those who met with the second set of 
phenomena were equally severe in their condemnation of 
this material. 

In all possibility this difference in the behavior of copper 
amalgam was due for the most part to the improper prepara- 
tion of the amalgam and, secondly, to the lack of proper care 
on the part of the operator in inserting the filling. 

Copper amalgam is used at the present time for the con- 
struction of small dies or models in swaging diaphragms 
for crowns, construction of models in the indirect method 
of cast inlay work and various other forms of dies in which 
light swaging is used. 

Copper is added to dental amalgam alloy to increase 
hardness and edge strength; it also aids in the setting qualities. 



PROPERTIES OF AMALGAMS 289 

It, however, has a tendency to cause the amalgam to discolor. 
In the percentage in which it is used in most amalgams 
this objection is more than overbalanced by the beneficial 
properties which it imparts. These three metals are agreed 
upon by all as being necessary constituents of dental 
amalgam alloys; however, other metals are added for the 
purpose of modifying color, aiding in the working properties 
and for various other reasons. 

The quantity of these additional metals rarely amounts to 
5 per cent, or over of the weight of the dental amalgam 
alloy. 

One of the great objections to adding too many metals 
in the production of the alloy is: as the number of metals 
present in an alloy increases, the difficulty of obtaining a 
homogeneous mass increases, and it must be borne in mind 
that each additional metal added just renders a homogeneous 
alloy that much harder to be obtained. The problem 
confronting us is simply this: "Does the addition of a certain 
metal with the properties which it imparts overbalance 
the difficulty of obtaining a homogeneous alloy?" 

Zinc. — This metal at the present time is looked upon with 
disfavor by some, claiming that it causes great but slow 
contraction. Others have not lost their faith in this metal, 
claiming it toughens the amalgam and also tends to lighten 
the color. 

Gold. — This metal has been discarded by most manufac- 
turers. However, there are some that still are of the belief 
that the properties which it imparts to the alloy cannot be 
dispensed with. Among the desirable properties which are 
claimed for this metal are: toughness, increased working 
properties, and that it produces good edge strength. 

Platinum. — Platinum is said to improve an amalgam when 
gold is present. . When gold is not present it does not possess 
any beneficial properties; on the other hand, it is deleterious, 
causing a slow setting and tendency to shrink. In amal- 
gamating such an alloy the hands are discolored or blackened 
by the presence of this metal. 
19 



290 AMALGAMS 

Palladium, bismuth, antimony, cadmium, produce more 
harmful than beneficial properties in these alloys. 

Cadmium forms an adhesive amalgam. However, it 
decomposes in the oral secretions with the formation of 
yellow cadmium sulphide, causing a yellow discoloration of 
tooth substance. 

The composition of dental amalgam alloy may approxi- 
mately be stated as follows: Silver 65, tin 30 and the various 
other metals making up the remaining five parts. If zinc is 
used it should not exceed 1 to 1.5 parts, while copper is 
permissible in a larger proportion. 

In the author's opinion gold and platinum may be dis- 
pensed with, as the complexity of the alloy is so much 
increased by the addition of these two metals that the 
properties reputed to them do not justify their addition. 
However, the usefulness of the metals gold, platinum, and 
even zinc is simply a matter of opinion, and there is no 
question but what alloys possessing these metals, if properly 
manipulated by the dentist, will produce all that may be 
desired. 



CHAPTER XXV. 
METHODS OF DRY ANALYSIS. 

A course of dry analysis, or so-called blow-pipe analysis, 
is of importance to the dental student for several reasons: 
(1) It imparts a thorough working knowledge of the Bunsen 
flame. (2) It teaches the use of the mouth blow-pipe and 
cultivates the art of proper breathing in the use of same. 

(3) It impresses upon his mind the various phases of oxidation 
and reduction that are possible during the process of heating. 

(4) It instills a knowledge of chemical reactions which differ 
materially from those produced by wet methods. 

Fusion. — The hottest portion of a flame is just beyond the 
tip of the blue flame. The reactive fusing point of the sub- 
stance should be treated in one of the following ways: 

(a) If metallic, heat on the charcoal block. 

(b) If stony or vitreous, hold in the Bunsen flame by means 
of platinum-pointed pliers. 

(c) If a powder, make a paste with water and allow to 
dry on charcoal block and then heat. 

Flame Coloration. — Use a platinum wire and hold in the 
flame of the Bunsen burner until all color disappears, then 
moisten the wire with some of the material; in some cases 
the color of the flame may be intensified by moistening a 
solid substance with a few drops of concentrated hydro- 
chloric acid. The colors will be given under each metal in 
the list which follows. 

Volatilization. — Some of the metals or their compounds are 
oxidized upon heating. The color of the sublimate or the 
odor produced is used to identify these substances. Vola- 
tilization tests are commonly obtained on charcoal, plaster, 
or in open and closed glass tubes. The reactions produced 
may be varied by the use of fluxes. Sodium carbonate or 
bismuth flux 1 may be used in these reactions. 

1 Two parts sulphur, one part potassium iodide, one part acid potassium 
sulphate. 



292 METHODS OF DRY ANALYSIS 

Bead Tests. — In these tests a loop is made in a platinum 
wire mounted in a glass rod. The agent used to form the 
bead is borax, or microcosmic salt (NaNH 4 HP0 4 ). The 
color of the bead produced varies, dependent upon the nature 
of the flame in which it is heated. 

Bulb Tube Tests. — These tests are performed in two 
ways: 1. By simply heating the substance in a bulb tube 
and noticing the changes produced, such as the gases given 
off, formation of a sublimate, or charring. 

2. Sulphuric acid may be added and the effects produced 
noted. 

The following is a list of the more common metals and their 
characteristic reactions as produced in this form of analysis : 

Antimony: 

On Charcoal, Reducing Flame — Volatile White Coat, 
Bluish in Thin Layers. 

With Bismuth Flux: 
On plaster: Peach-red coat. 
On charcoal: Faint yellow or red coat. 
In open tube: Dense, white, non- volatile, amorphous 

sublimate. 
Flame: Pale yellowish green. 
Arsenic: 
On smoked plaster: White coat crystalline. 
On charcoal block: Very volatile, white coat and strong 

garlic odor. 
With Bismuth Flux: 

On plaster: Reddish-orange coat. 

On coal: Faint yellow coat. 
Bismuth: 
On charcoal: In either flame, a brittle metal and 

volatile; coat, dark orange-yellow, hot lemon-yellow, 

cold with yellowish-white border. 
With Bismuth Flux: 

On plaster: Bright scarlet coat, surrounded by choc- 
olate brown. The brown may be made by ammonia. 



BULB TUBE TESTS 293 

Aluminum: 
With sodium carbonate : Swells and forms an infusible 

compound. 
With borax: Bead clear or cloudy, never opaque. 
With cobalt solution and heated with blow-pipe : Fine 

blue color when cold. 
Cadmium: 
On charcoal, reducing flame: Dark brown coat, greenish 

yellow in thin layers. 
On smoked plaster with bismuth flux: White coat made 

orange with ammonium sulphide. 
Copper: 
On coal with reducing flame : Formation of red malleable 

metal. 
Flame: Emerald green or azure blue. 

If the compound be moistened with hydrochloric 
acid the Azure-blue flame is produced. 
With borax bead: Oxidizing flame. Green, hot, blue or 

greenish blue, cold. 
Reducing flame : Greenish or colorless hot, opaque, and 

brownish red, cold. 
Iron: 
On charcoal, reducing flame : Many compounds become 

magnetic, sodium carbonate assists the reaction. 
With borax beads : Oxidizing flame. Yellow to red, hot, 

colorless to yellow, cold. 
Reducing flame: Bottle green. 
Lead: 

On charcoal: In either flame is reduced to malleable 

metal and may have lemon-yellow coating surrounding 

the lead button. 
With Bismuth Flux: 

On plaster: Chrome-yellow coat, blackening with 
ammonium sulphide. 

On charcoal: Volatile yellow coat. 

Flame: Azure blue. 



294 METHODS OF DRY ANALYSIS 

Lithium: 

Flame : Crimson, best obtained by heating near center 
of the flame. 
Magnesium: 

On charcoal with sodium carbonate : Insoluble, and not 

absorbed by the coal. 
With Cobalt solution: Strongly heated becomes a pale 
flesh color. 
Manganese: 
With Borax Beads: 

Oxidizing flame: Amethyst color, hot, reddens on 

cooling. 
Reducing flame : Colorless or with black spots. 
With sodium carbonate and potassium nitrate bead: 
Oxidizing flame : Bluish green and opaque when cold. 
Mercury: 

With Bismuth Flux: 

On plaster : Volatile yellow and scarlet coat if strongly 

heated; coat is black and yellow. 
On charcoal : Faint yellow coat at a distance from the 
depression in the charcoal. 
Nickel: 
On charcoal reducing flame: The oxide becomes mag- 
netic. 
With borax bead: 

Oxidizing flame : Violet, hot, pale reddish, cold. 
Reducing flame : Cloudy and finally clear and colorless. 
Potassium: 

Flame: Violet. 
Silver: 
On Charcoal: Reduction to a malleable white metal. 
Dissolve button in HN0 3 , dilute and add ammonium 
hydroxide slowly until the brown precipitate which 
first forms just dissolves, add 2 drops of solution of 
formaldehyde and heat in test-tube; mirror of silver 
will be produced. 
Sodium: 
Flame: Strong yellow flame, not visible through cobalt 
glass. 



BULB TUBE TESTS 295 

Strontium: 
Flame: Intense crimson, improved by moistening with 
HCL 
Tin: 
On charcoal: 

Oxidizing flame: The oxide becomes yellow and 
luminous; when the oxide is moistened with cobalt- 
ous nitrate and heated with reducing flame the coat 
will be bluish green when cold. 
Zinc- 
On charcoal: 

Oxidizing flame: The oxide becomes yellow and 
luminous while hot and upon cooling is colorless. 
When oxide is moistened with cobalt-nitrate solution 
and heated in reducing flame, the coat is yellowish 
green when cold. 
The following is a systematic scheme for qualitative 
blow-pipe analysis: 
Test I. — Heat a portion of the substance gently with the 
oxidizing flame upon a charcoal block or a plaster tablet 
which has been blackened in the lamp flame. Arsenic 
and antimony will be recognized by the white coating. 
Test II. — Mix some of the substance with metallic 
sodium by means of a knife blade, ignite carefully on 
charcoal and heat residue with blow-pipe flame to 
obtain coating or to fuse together any metallic particles. 
Or mix a portion with soda and a little borax and heat 
strongly upon charcoal with reducing flame for three 
or four minutes. Arsenic, antimony, cadmium, zinc, and 
tin will be recognized by their characteristic reactions. 
Residue Left on Charcoal. 
Crush and examine for (1) magnetic particles; (2) 
metallic buttons ; (3) place some of residue on silver 
coin. 

1. Will show iron, nickel or cobalt. 

2. Will show silver, lead, tin, copper, gold, bismuth or 

antimony. 

3. Will show sulphur, selenium, tellurium. 



296 METHODS OF DRY ANALYSIS 

Test III. — Mix substance with a larger quantity of 
bismuth flux and heat on plaster tablet with oxidizing 
flame. Lead, mercury, bismuth, and antimony will 
show characteristic colorations. 

Test IV. — Dissolve the substance in microcosmic salt 
bead in the oxidizing flame, then heat three or four times 
in the reducing flame; note colors hot and cold, then 
reoxidize and note colors hot and cold. 

Iron,- Titanium, Molybdenum and Tungsten: The bead 
in oxidizing flame, cold is colorless or faint yellow. 

Uranium, Vanadium and Nickel: The bead in oxidizing 
flame, cold is yellow or greenish yellow. 

Manganese: The bead in oxidizing flame, cold is colored 
violet. 

Chromium : In oxidizing flame is colored green. 

Copper and Cobalt: In oxidizing flame is colored blue. 

Barium, Calcium, Strontium, Magnesium: In oxidizing 
flame give white opaque beads. 

Test V. — Cupellation for silver and gold. Fuse one 
volume of the roasted substance on charcoal with one 
volume of borax glass and one or two volumes of test 
lead in reducing flame for about two minutes. Remove 
button and scorify it in reducing flame with fresh borax ; 
then place button on cupel and blow oxidizing flame 
across it, using as strong blast and as little flame as are 
consistent with keeping the button melted. If the oxide 
of lead formed is dark or if the button freezes before 
brightening, scorify it again with borax and add more 
test lead, again cupel until there remains only a bright 
spherical button, unaltered by further blowing. If 
silver is present, the button is white, while if gold is 
present, the button is yellow or white. 

Test VI. — Heat substance with acid potassic sulphate. 
Oxides of nitrogen, bromine, chlorine and iodine will be 
recognized by their odor. 

Test VII. — Heat the substance gently with water to 
remove air and then add dilute hydrochloric acid. 
Carbon dioxide, hydrogen sulphide and hydrogen may 
be given off 



BULB TUBE TESTS 



297 



Test VIII. — Make a paste of the powdered substance with 
strong hydrochloric acid. Treat on platinum wire in the 
non-luminous flame of the Bunsen burner. 

The colors produced are: 



Metal. 



Color. 



Color through cobalt glass. 



Sodium 


Yellow 


Invisible. 


Potassium 


Violet 


Reddish violet. 


Sodium and potassium 


Yellow 


Reddish violet. 


Barium 






Molybdenum > 


Yellowish green 


Bluish green. 


Boron J 






Calcium 


Red 


Greenish gray. 


Strontium 


Scarlet 


Violet. 


Copper 


f Azure blue 
\ Emerald green 


( Azure blue. 
\ Emerald green. 



Test IX. — Heat the substance in a closed tube: 
Water: Moisture in the side of tube. 
Mercury: Metallic mirror collecting in globules. 
Arsenic: Metallic mirror, no globules. 

Test X. — Treat finely powdered substance in test-tube 
with strong hydrochloric acid. 
Effervescence: Carbon dioxide, hydrogen sulphide, sul- 
phur dioxide, or hydrochloric acid may be given off; a 
gelatinous residue indicates a silicate. 



CHAPTER XXVI. 
WET METHOD OF ANALYSIS. 

In analyzing an alloy, the first procedure is to obtain a 
solution of the alloy with some suitable solvent. Hydro- 
chloric or sulphuric acids, both dilute or concentrated, may 
be tried and if they fail to dissolve the alloy, then nitric acid 
may be tried. • When nitric acid is used the solution should be 
evaporated to dryness in order to drive off the excess of the 
acid, as it would interfere with the action of hydrogen 
sulphide. 

Alloys containing antimony and tin will produce a white 
precipitate when nitric acid is used, due to the formation of 
oxides of these metals. In such an alloy hydrochloric acid 
should be used first to dissolve these metals, and if the alloy 
is not entirely soluble then the metallic residue may be treated 
with nitric acid and dissolved. The outline for the separation 
of the metals is based upon the following reaction of them to 
certain reagents: 

Hydrochloric acid precipitates silver, lead (partially) and 
mercurous mercury as the chlorides. Hydrogen sulphide in 
an acid solution throws down the following metals: bismuth, 
copper, cadmium, mercuric mercury, arsenic, antimony, tin, 
gold and platinum. 

Hydrogen sulphide in an alkaline solution precipitates 
iron, aluminum, chromium, cobalt, nickel, manganese and 
zinc. 

Ammonium carbonate precipitates barium, strontium, and 
calcium. The remaining metals, sodium, potassium, lithium 
and magnesium require special treatment in order to identify. 

A confirmatory test is one that is used to positively identify 
a metal by the use of some special reagent. They are some- 



ANALYTICAL PROCEDURE 299 

times spoken of as " a test for the metal." To illustrate: 
potassium ferrocyanide in an acetic acid solution is a con- 
firmatory test for copper. If it is desirable to make a simple 
test for one metal as in the case of a salt, or one wishes to 
determine if some particular metal is present, all that is 
necessary is to turn to the general analysis and use the 
reagents of some particular metal. 



Gkoup I. 

Three metals are included under this heading, namely: 
lead, mercury in the mercurous condition designated as 
Hg 2 ; silver, Ag; they are alike in their behavior toward 
hydrochloric acid, HC1. This reagent added to a solu- 
tion of one or more of these metals causes a white pre- 
cipitate. Pb appears as white plumbic chloride, PbCl 2 , 
slightly soluble in cold but more soluble in hot water. Hg 2 
as white mercurous chloride (calomel), Hg 2 Cl 2 , insoluble in 
hot or cold water, and Ag as white argentic chloride, AgCl, 
insoluble in hot or cold water. They may be identified by 
characteristic precipitates. Pb forms white insoluble plumbic 
sulphate, PbS0 4 ,Hg 2 , black, insoluble mercurous amido 
chloride, Hg 2 H 2 NCl, and white, insoluble AgCl. 

Analytical Procedure. — Put 50 c.c. of cold solution of these 
metals into a 100 c.c. beaker and cautiously add concentrated 
HC1 until a drop fails to cause a precipitate. Let stand 
five minutes. Filter into a 250 c.c. flask and keep the filtrate 
for the next group. The precipitate consists of the chlorides 
of group I metals; wash it once with cold water and reject 
the wash water. Next wash with 25 c.c. of hot water, passing 
it through the paper two or three times, PbCl 2 dissolves; 
cool the solution in a test-tube and add a few drops of dilute 
H 2 S0 4 . If Pb is present, white insoluble PbS0 4 will appear. 

Pour over the remaining precipitate, which is insoluble in 
hot water, 15 c.c. of ammonic hydroxide, (H 4 N)OH, passing 
it through the paper two or three times. Hg 2 Cl 2 , if present, 
is converted into a black Hg 2 H 2 NCl. 



300 



WET METHOD OF ANALYSIS 



Note. — Hydrogen sulphide, H 2 S, when present in the 
atmosphere of the laboratory, often causes a slight darkening 
even when Hg 2 Cl 2 is absent. A distinction, therefore, must 
be made between the pronounced black of Hg 2 H 2 NCl and 
any slight change of color by H 2 S. At the same time that 
(H 4 N)OH produces this black compound it dissolves AgCl. 

Note. — If any PbCl 2 remains because of incomplete wash- 
ing with hot water (H 4 N)OH will change to insoluble white 
basic plumbic chloride, PbCl 2 .Pb(OH) 2 , which renders the 
filtrate milky; as this does not interfere with the final test 
for Ag it may be disregarded. 

Add cone. HN0 3 to the filtrate until all (H 4 N)OH is 
neutralized and the solution is acid ; Ag, if present in quantity, 
appears as white, curdy AgCl; traces cause an opalescence. 

Group II. 

Ten metals, divided into subgroups A and B, are included 
under this heading, viz. : 



Subgroup A. 



Subgroup B. 



1. Mercury in the mercuric condition designated as Hg. 

2. Lead, Pb. 

3. Bismuth, Bi. 

4. Copper, Cu. 

5. Cadmium, Cd. 

6. Arsenic, As. 

7. Antimony, Sb. 

8. Tin (a) Stannous SnII; (b) Stannic SnIV. 

9. Gold, Au. 
10. Platinum, Pt. 



They 
H 2 S, as 
solution 
namely : 



are alike in their behavior toward hydrogen sulphide, 

they are precipitated by this reagent from an acid 

Under these conditions sulphides are formed, 



Subgroup A. 



Subgroup B. < 



1. Hg appears as black mercuric sulphide, HgS. 

2. Pb appears as black plumbic sulphide, PbS. 

3. Bi appears as brown-black bismuthous sulphide, Bi2S3. 

4. Cu appears as black cupric sulphide, CuS. 

5. Cd appears as yellow cadmic sulphide, CdS. 

6. As appears as yellow arsenous sulphide, AS2S3. 

7. Sb appears as orange-red antimonous sulphide, Sb2S3. 

8. SnII appears as chocolate-brown stannous sulphide, SnS. 

9. SnIV appears as yellow stannic sulphide, SnS2. 

10. Au appears as brown sulphide, AU2S or AU2S2. 

11. Pt appears as black sulphide, PtS or PtS2. 



ANALYTICAL PROCEDURE 301 

They may be identified by characteristic tests, viz.: 

Subgroup A: (1) Hg, bv (a) Hg globules: (b) white ppt. 
Hg 2 Cl 2 . (2) Pb, bv white ppt. PbS0 4 . (3) Bi, bv white ppt. O 
=Bi-Cl. (4) Cu, by (a) blue CuS0 4 ,5H 3 X; (6) red-brown 
ppt. Cu 2 Fe(CX) 6 . (5) Cd, by yellow ppt. CdS. 

Subgroup B: (6) As, by shiny brown-black mirror. (7) 
Sb, by orange-red ppt. Sb 2 S 3 . (8) SnII and SnIV, by white 
ppt. with Hg 2 Cl 2 . (9) Au, by precipitate with stannous and 
stannic chlorides (purple of Cassius). (10) Pt, by yellow ppt. 
with (H4X)C1 ammonic chlorplatinate. 

Analytical Procedure. — The filtrate in a 250 c.c. flask from 
the HC1 ppt. should be gently warmed upon the iron plate; 
or a solution free from the bases of group I should be acidified 
with HC1 and treated in the same way. Xext pass H 2 S 
through the solution until it smells strongly of the gas after 
being thoroughly shaken. The metals of group II are pre- 
cipitated as sulphides. 

Note. — Complete ppt. is important, the solution must not 
be too strongly acid. An excess of H 2 S must be used. Filter, 
add a few cubic centimeters water, warm gently and again 
treat with H 2 S. If there is no ppt. the next step may be taken, 
otherwise dilute the remaining solution and pass more H 2 S 
through it; this must be repeated until ppt. is complete. 
Filter into a 250 c.c. flask and keep the filtrate for group III. 
The color of the ppt. may indicate the presence or absence of 
certain metals. If it is black no information is given beyond 
the fact that at least one of the black sulphides is present. 
If it is yellow, black sulphides are absent except, possibly, 
in traces, and the color is due to Cd, As, Sb, or SnIV. Wash 
the ppt. three times with boiling water and transfer it to a 
small dish. 

Note. — The method of procedure from this point 
depends upon whether metals of both subgroups or of one 
are present. 

Procedure when Both Groups are Present. — Pour over the 
ppt. 15 to 25 c.c. of yellow ammonic disulphide, (H 4 X) 2 S 2 , 
warm on the steam bath for five minutes and then stir 
frequently. This reagent dissolves subgroup B sulphides 



302 WET METHOD OF ANALYSIS 

but not those of subgroup A. Filter into a small beaker and 
keep the filtrate for subgroup B tests. Wash the ppt. with 
hot water three times. Transfer it to a small dish and make 
subgroup A tests. 

Procedure when Subgroup A Alone is Present. — When sub- 
group B has been removed pour over the ppt. 15 to 25 c.c. 
of dilute HN0 3 and then add the same volume of water. 
Warm on the steam bath for ten minutes and stir frequently; 
all of the sulphide of subgroup A except HgS are dissolved. 
Filter into a beaker. Add to the filtrate 5 c.c. of diluted 
H2SO4, pour it into a small dish and evaporate on the iron 
gauze until all HN0 3 has been expelled and the solution has 
nearly reached dryness. During this evaporation examine 
the ppt. for Hg. Wash it once with hot water. If the ppt. 
is not black but yellow, Hg is absent and the ppt. is sulphur. 
On the other hand, a black ppt. is not sufficient proof of Hg, 
since sulphur mixed with some undissolved sulphides other 
than HgS may be taken for HgS. Two tests are available 
for confirming the presence of Hg. 

Copper Wire Test for Hg. — Put a few crystals of potassic 
chlorate, KC10 3 , into a test-tube and add 5 c.c. of cone. HC1, 
warm and pour over the HgS. Collect the acid solution in 
another test-tube and pass it through the paper two or three 
times until nothing but sulphur remains. Dilute the acid 
solution with the same volume of water and divide it into 
two portions, keep one portion for the next test for Hg. 
Place in the other a bright piece of copper wire, remove the 
wire after five minutes and dry it on the filter paper. Place 
it in a bulb tube and heat it; with a lens examine the cool 
part of the tube for globules of Hg which prove the presence 
of this metal in the mercuric condition. 

Stannous Test for Hg. — To the reserved portion of the 
dilute acid solution add a few drops of a solution of stannous 
chloride, SnCl 2 ; a white ppt. of Hg 2 Cl 2 often darkened by Hg 
proves the presence of Hg in the mercuric condition. 

Return to the solution which has been evaporating, 
transfer it to a small beaker and wash any ppt. from the dish 
with cold water. A white ppt. is PbS0 4 and it is due to Pb 



ANALYTICAL PROCEDURE 303 

not completely removed by HC1 in group I. Note: If Pb 
is found in group I it must appear here also, otherwise there 
has been some error in procedure. Pb when present in small 
amount may fail to appear in group I and yet appear in 
group II. If present and not removed it may cause trouble 
later in the analysis. Filter to remove PbS0 4 and collect 
the filtrate in a small beaker. Add (H 4 X)OH until the 
solution is alkaline. This reagent may produce two results, 
namely : 

(a) It may turn the solution blue, which is positive proof 
of the presence of Cu. (b) It may cause a flocculent ppt., 
which is an indication of Bi. Note: Cu may be present in 
such small amount that (H 4 N)OH will not give the test. In 
this case the KiFe(CN)6 test must be made. If (H 4 N)OH 
does not cause a ppt., Bi is absent. On the other hand a 
ppt. must not be accepted as proof of Bi until the confirmatory 
test has been made. Filter and collect the filtrate in a test- 
tube. If the filtrate is not blue take one-third of it and 
acidify with acetic acid (HC 2 H 3 2 ). Add a few drops of 
a solution of K 4 Fe(CN) 6 ; a red-brown ppt. or coloration is 
due to cupric ferrocyanide, Cu 2 Fe(CN) 6 , and proves the pres- 
ence of Cu; keep the remaining two-thirds of the filtrate for 
the Cd test. 

Wash the ppt. which may be bismuthous hydroxide, 
Bi(OH) 3 , twice with hot water. Set the funnel in a test-tube 
and pour over the ppt. five drops of cone. HO. Pass it 
through the paper two or three times until the ppt. is dissolved. 
Add one drop of this solution to a test-tube full of water. 
A white ppt. is bismuthous oxychloride, BiOO, and proves 
the presence of Bi. 

Return to the remaining two-thirds of the filtrate and test 
it for Cd. If Cu has not been found by either test, pass the 
H 2 S through the filtrate and a yellow ppt. of CdS appears if 
Cd is present. On the other hand, if Cu has been found by 
either test, add to the solution a few pieces of solid potassic 
cyanide, KCN. 

If the solution is blue, enough KCX should be used to 
discharge the color. Pass H 2 S through the solution. Yellow 



304 WET METHOD OF ANALYSIS 

CdS appears if Cd is present, but fuS is not ppt. in the 
presence of KCN. 

Note. — In testing for Cd it often happens the ppt. is black 
instead of yellow. This arises from some error of manipula- 
tion resulting in the incomplete removal of one or more of 
the metals having black sulphides. Collect the ppt. on a 
filter paper of the smallest size and wash it twice with boiling 
water. Place the ppt. and paper in a dish and add 5 c.c. of 
diluted HN0 3 ; further dilute with the same volume of water. 
Warm on the water-bath, filter and evaporate with diluted 
H 2 S0 4 , proceed as previously directed for removal of Pb and 
Bi. Finally pass H 2 S through the solution, which has been 
rendered alkaline with (H 4 N)OH. 

Procedure when Subgroup B Alone is Present or when 
Subgroup A has been Removed. — Put into a small beaker 
the solution of the sulphides of subgroup B in yellow (H 4 N) 2 S 2 
and cautiously add diluted HC1 until the solution is acid. 
If present arsenious sulphide, As 2 S 3 , will be ppt. yellow; 
antimonous sulphide, Sb 2 S 3 , orange-red, stannic sulphide, 
SnS 2 , yellow, Au 2 S brown, PtS black. If only a white ppt. 
of sulphur appears the metals of subgroup B are absent. 

Note. — Sn, whether present in the original solution in the 
stannous or in the stannic condition, will always appear at 
this point as stannic sulphide, SnS 2 , because both SnS and 
SnS 2 when dissolved in yellow (H 2 N) 2 S 2 form the same 
compound. 

If the ppt. is yellow or orange red, filter and wash it twice 
with hot water. If the presence of gold or platinum is sus- 
pected, dissolve the precipitate in hydrochloric acid con- 
taining a few crystals of potassium chlorate, evaporate to 
remove chlorine, then add KOH and boil, add some chloral 
hydrate to the solution and Au and Pt will be precipitated. 
Filter and wash with warm water, then dissolve ppt. in aqua 
regia (1 prt HN0 3 +3 prts HO), evaporate solution containing 
Au and Pt nearly to dryness, dilute with water, add to a 
portion of the solution stannous chloride containing a little 
stannic chloride, a purple ppt. confirms the presence of gold. 
To the balance of the solution containing Au and Pt add 



ANALYTICAL PROCEDURE 305 

(H 4 X)OH until it is nearly neutral to test papers, then add 
(H 4 X)C1; if Pt is present it will be precipitated as black 
metallic platinum. 

Return to the solution from which Au and Pt were pre- 
cipitated with chloral hydrate, acidify with HC1 and again 
pass H 2 S through the solution, filter and wash twice with hot 
water. 

Pour 10 c.c. of a concentrated solution of ammonic car- 
bonate, (H 4 X) 2 C0 3 , upon the ppt. As 2 S 3 , if present, will be 
dissolved, in order to remove As 2 S 3 completely, pass the 
solution through the paper several times. Put the solution 
into a small beaker and add cone. HX0 3 until it is acid. 
As 2 S 3 , if present, will be ppt. If there is no ppt., As is absent. 
On the other hand, a ppt. must not be accepted as positive 
evidence of As. 

Put the solution and ppt. into a small dish and evaporate 
to complete dryness under the hood. When the residue is 
cool, thoroughly mix it in a mortar with an equal quantity 
of a mixture consisting of sodic carbonate, Xa 2 C0 3 , and 
potassic nitrate, KX0 3 . Place some of the mixture upon a 
piece of platinum foil and with the iron pincers hold in the 
name of the Bunsen burner until the mass fuses. Cool and 
place the platinum foil in a porcelain dish and add 10 c.c. 
of water, then place the dish on the iron gauze and heat to 
boiling. Cool and cautiously add a few drops of cone. HX0 3 
until the solution is strongly acid. Remove the platinum 
foil from the liquid and add 5 c.c. of ammonic molybdate 
solution, heat gently; a yellow ppt. indicates the presence 
of As. Return to the residue insoluble in (H 4 X") 2 C0 3 . Wash 
it once with hot water. Put some KC10 3 into a test-tube 
and add 5 c.c. of cone. HC1. Warm the solution and pour it 
upon the ppt. Collect it in another test-tube and pass it 
through the paper several times. It will dissolve Sb 2 S 3 and 
SnS 2 . Dilute the solution with twice its volume of water 
and put it into a large beaker. Place some iron tacks into 
the solution and let stand for fifteen minutes under the hood. 
Sb will be deposited in the metallic condition as a black 
coating or residue and the Sn will remain in solution. Special 
20 



306 WET METHOD OF ANALYSIS 

tests must be made for both metals. Filter and collect the 
filtrate in a test-tube. To confirm Sn, boil the filtrate for a 
few minutes then dilute with water until the volume is 20 
c.c, and add a solution of HgCl 2 ; a white ppt. darkening 
upon standing indicates the presence of Sn. 

To confirm the presence of Sb, wash the residue upon the 
paper several times with hot water then pour on the paper a 
solution of tartaric acid, (H 2 C4H 4 6 ), containing three drops 
of cone. HN0 3 . Evaporate the washings to almost dryness, 
cool and add water until the residue dissolves; add a few 
drops of cone. HC1 and pass H 2 S through the solution; an 
orange red indicates Sb. 

Group III. 

Introduction. — Seven metals are included under this head- 
ing, viz.: (1) Cobalt, Co; (2) Nickel, Ni; (3) Iron, Fe; 

(4) Aluminum, Al; (5) Chromium, Cr; (6) Manganese, Mn; 
(7) Zinc, Zn. 

They are alike in their behavior toward ammonic sulphide, 
(H 4 N) 2 S, as they are precipitated by this reagent from a 
neutral or alkaline solution under these conditions excepting 
in the case of Al and Cr, which appear as hydroxides, sul- 
phides are formed, viz. : (1) Co appears as black cobaltous 
sulphide, CoS. (2) Ni appears as black nickelous sulphide, 
NiS. (3) Fe appears as black ferrous sulphide, FeS. (4) Al 
appears as white gelatinous aluminic hydroxide, Al(OH) 3 . 

(5) Cr appears as gray-green gelatinous chromic hydroxide, 
Cr(OH) 3 . (6) Mn appears as flesh-colored manganous 
sulphide, MnS. (7) Zn appears as gray-white zinc sulphide, 
ZnS. 

They, may be identified by characteristic tests, viz. : (1) 
Co by blue bead with anhydrous borax, Na 2 B 4 07. (2) Ni by 
black ppt. Ni(OH) 3 . (3) Fe by testing original solution, 
viz.: (a) ferrous gives deep blue ppt. with K 6 Fe 2 (CN)i 2 ; 

(6) Ferric gives deep blue ppt. with K 4 Fe(CN) 6 . (c) Ferric 
gives blood-red solution with KSCN. (4) Al by white, 



ANALYTICAL PROCEDURE 307 

gelatinous ppt. Al(OH) 3 . (5) Cr by yellow ppt. PbCr0 4 . 
(6) Mn by blue-green bead with Na 2 C0 3 and KN0 3 . (7) 
Zn by gray-white ppt. ZnS from acetic acid solution. 

Analytical Procedure. — Warm gently upon the iron plate 
in 500 c.c. flask, place the filtrate from the H 2 S ppt. or a solu- 
tion free from the bases of groups I and II. Add 10 c.c. of solu- 
tion of amnionic chloride, (H 4 N)C1, next make the solution 
slightly alkaline with (H 4 N)OH, avoiding a large excess, 
as it interferes with the complete ppt. of Ni. If H 2 S is in the 
solution (H 4 N)OH will convert it into (H 4 N) 2 S; as a result 
a black ppt. will appear if any metal having a black sulphide 
is present, also in the absence of H 2 S the hydroxides of Fe, 
Cr, and Al will be ppt. by (H 4 N)OH if these metals are present. 
Disregard any ppt. (H 4 N)OH may cause. Finally add 10 c.c. 
of solution of ammonic sulphide, (H 4 N) 2 S. Cork the flask 
tightly and wrap a towel around it and shake vigorously 
for two minutes, filter a few cubic centimeters of the solution 
and add a drop of (H 4 N) 2 S to see if ppt. is complete. If it 
is not complete add 5 c.c. of (H 4 N) 2 S. Cork, shake and test 
again. This should be repeated until ppt. is complete. All 
of the metals of group III will have been ppt. Filter into 
a small flask and keep the filtrate for group IV; make this 
filtration as quickly as possible and at the same time keep 
the ppt. from contact with air. Use a pleated filter and keep 
the funnel full with hot water to which a little (H 4 N) 2 S has 
been added. When the main part of the filtrate has been 
collected, set it aside and reject the wash water. Set the 
funnel holding the wash ppt. into a 250 c.c. flask, with a glass 
rod punch a hole through the paper and wash the ppt. into 
the flask with cold water. Cool thoroughly, add 10 c.c. of 
dilute HC1 or enough to make the solution acid and shake 
well. Dilute HC1 will dissolve everything except CoS and 
NiS. The color of the ppt. may give some indication as to 
what is present. A black ppt. shows that one or more of the 
metals having black sulphides is present. The black ppt., 
completely soluble in dilute HC1, shows that Fe is present 
and that Co and Ni are absent. A black ppt. incompletely 
soluble in dilute HC1 shows positively that Co and Ni, 



308 WET METHOD OF ANALYSIS 

one or both, are present and that Fe may be. If it is not 
black, Co and Ni and Fe are absent. If dilute HC1 does not 
completely dissolve the ppt., filter. Put the filtrate into a dish, 
add 5 c.c. of cone. HN0 3 and evaporate over the iron gauze 
to concentrate the solution and expel all H 2 S. 

The ppt. may contain CoS and NiS. Wash it well with hot 
water; make a perfectly clear bead of powdered borax, 
Na 2 B 4 7 , on a small loop of platinum wire. Touch the bead 
to the ppt., taking care not to get too much on it, and fuse 
again until the bead is perfectly clear. Under these con- 
ditions both Co and Ni give colored beads. The Co bead is 
blue and will always mask the Ni bead which is reddish 
brown in the oxidizing, and gray in the reducing flame. If 
Co is absent the ppt. must be due to Ni. If Co is present a 
special test must be made for Ni, and it is generally advisable 
to make it anyway. Make, in a test-tube, a mixture of 6 c.c. 
of cone. HC1 and 2 c.c. of cone. HN0 3 . Warm gently and 
pour it over the washed sulphide upon the paper, passing 
it through the paper several times CoS and NiS are dis- 
solved. Pour the solution into a beaker and make it alkaline 
with NaOH; Co(OH) 2 and Ni(OH) 2 are ppt.; filter, using 
paper of the smallest size and wash the ppt. with hot water; 
put 5 c.c. of water into a test-tube and make a strong solution 
of KCN. Set the funnel in a test-tube and pour the solution 
over the ppt., passing through the paper until everything is 
dissolved. KCN converts Ni(OH) 2 into Ni(CN) 2 2KCN, 
a double cyanide of Ni and K; Co(OH) 2 into KeCo 2 (CN)i 2 , 
potassic cobaltic cyanide. Add to the solution a few drops 
of NaOH and then bromine water in large excess. Co remains 
unchanged but Ni undergoes oxidation, which results in the 
formation of nickelic hydroxide, Ni(OH) 3 . This appears as a 
black ppt. or more frequently as a black ring at the zone of 
contact of the KCN solution with the bromine water. Heat 
sometimes facilitates the reaction. Return to the solution 
which has been evaporating in a dish, transfer it to a beaker, 
cool thoroughly and neutralize the acid with dry Na 2 C0 3 . 
It is necessary that the solution be slightly acid. If a per- 
manent ppt. is formed because too much Na 2 C0 3 has been 



ANALYTICAL PROCEDURE 309 

used, cautiously add dilute HC1, drop by drop, until the ppt. 
is entirely dissolved. If the presence or absence of phosphates 
and oxalates has not been determined, this must now be 
settled before the next step is taken, as these substances 
interfere with the regular course of basic analyses. 

Phosphates. — Mix 5 c.c. of the original solution with 
5 c.c. of cone. HX0 3 and then add 10 c.c. of amnionic 
molybdate solution, (H 4 X) 2 Mo0 4 ; a yellow ppt. of phospho- 
molybdic acid appears in the cold. If the quantity of phos- 
phate is small the ppt. forms upon standing. 

Oxalates.?, — Add to 5 c.c. of the original solution enough 
dry Xa 2 CO to render the solution strongly alkaline and boil 
for five minutes. Filter; acidify the filtrate with H(C 2 H 3 02) 
and boil it to expel C0 2 . Cool and add a few drops of solu- 
tion of calcic chloride, CaCl 2 . A white ppt. of calcic oxalate, 
CaC 2 4 , will appear if oxalic acid is present. 

Procedure tvhen Phosphates and Oxalates are Absent. — 
Add to the nearly neutral solution 25 c.c. baric carbonate, 
BaC0 3 , suspended in water. Set aside for fifteen minutes 
and stir occasionally; BaC0 3 ppt. Fe, Al and Cr as hydroxide, 
but it has no action on Mn or Zn. Filter and keep the 
filtrate for the Mn and Zn tests. 

The ppt. of the hydroxides of Fe, Al and Cr, together with 
the excess of BaCO?, must first be washed with hot water. 
Then set the funnel in a test-tube and pour dilute HC1 over 
the ppt., passing it through the paper until everything is 
dissolved. Make the solution alkaline with (H 4 X)OH which 
will ppt. the hydroxides of Fe, Al and Cr free from Ba. 
Filter, wash the ppt. with hot water and dry thoroughly 
without burning, by setting the paper in a funnel and pouring 
5 c.c. of cone. HXO3 over it, passing it through the paper until 
everything is dissolved. Add to the solution a few crystals 
of KCIO3 and warm gently; Cr. which is present in the basic 
condition as chromic nitrate, Cr(X0 3 )3, is oxidized and there- 
by converted into the acid condition as chromic anhydrite, 
Cr0 3 . Cr in the basic condition gives green solutions. When 
the change has been brought about, the color should be 
reddish yellow. When oxidation is complete make the solu- 



310 WET METHOD OF ANALYSIS 

tion alkaline with NaOH. If Fe is present, it will appear as 
a reddish-brown ppt. of ferric hydroxide, Fe(OH) 3 . 

Al will not appear as Al(OH) 3 , because in the presence of an 
excess of NaOH it is converted into sodic aluminate, Al (ONa) 3 , 
which is soluble in water. Cr in the acid condition is not 
ppt. by NaOH, but Cr0 3 is converted into sodic chromate, 
Na 2 Cr04, which is soluble in water. If there is a ppt. filter 
and ascertain by testing the original solution whether Fe is 
present in the ferrous or ferric condition. It is necessary to 
test the original solution, because processes of oxidation and 
reduction have been used in the analytical procedures as a 
result of which Fe is changed. Keep the filtrate for the Al 
and Cr tests. Two tests are available for Fe in the ferric 
and one for the ferrous conditions: Potassic ferrocyanide, 
K 4 Fe(CN) 6 , test for ferric iron; add to 5 c.c. of the original 
solution a few drops of dilute HC1 and then a few drops of 
K<iFe(CN) 6 . This reagent produces a light blue ppt. with 
ferrous Fe, but ferric compounds give a deep blue ppt. of 
"Prussian blue" or ferric ferrocyanide, Fe 2 (Fe(CN) 6 ) 3 . It 
is necessary to discriminate between the two precipitates. 

Potassic Sulphocyanate, KSCN, Test for Ferric Iron. — Add 
to 5 c.c. of the original solution a few drops of dilute HC1 
and then a few drops of KSCN or (H 4 N)SCN. Ferric Fe 
produces a deep blood-red coloration due to Fe(SCN) 3 . 

Potassic Ferricyanide, K G Fe2(CN) 12 , Test for Ferrous Iron. — 
Add to 5 c.c. of the original solution a few drops of dilute 
HC1 and then a few drops of K 6 Fe(CN)i 2 . This solution 
should be freshly prepared each time a test is made as it 
changes on standing. 

Ferrous FeS, produces a deep blue ppt. of "Turnbull 
Blue" or ferrous ferricyanide, Fe 3 (Fe 2 (CN)i 2 ). 

Divide into two equal portions the filtrate which may 
contain Al and Cr, add to one portion twice its volume of 
(H 4 N)C1, and heat to boiling. Al if present will appear as a 
white gelatinous ppt. or Al(OH) 3 ; render the second portion 
acid with H(C 2 H 3 2 ) and then add a few drops of a solution 
of plumbic acetate, Pb(C 2 H 3 2 ) 2 . Cr if present will appear 
as yellow ppt. plumbic chromate, PbCr0 4 . 



ANALYTICAL PROCEDURE 311 

Return to the filtrate which may contain Mn and Zn. Pour 
it into a beaker and heat nearly to boiling on the iron plate. 
Stir and add dilute H 2 S0 4 until a drop ceases to cause a 
white ppt. The object of this step is to free the solution 
from Ba which came from the BaC0 3 that caused the ppt. 
of Fe, Al, and Cr. Filter to remove BaS0 4 , render the filtrate 
alkaline with NaOH and boil five minutes. Mn if present 
will be precipitated as flocculent, flesh-colored, manganous 
hydroxide, Mn(OH) 2 . Upon standing, especially if exposed 
to the air, Mn(OH) 2 undergoes oxidation and the color changes 
to brown owing to the formation of manganic oxy hydroxide, 
Mn 2 2 (OH) 2 . Zn, on the other hand, is not ppt. because 
Zn(OH) 2 in the presence of an excess of NaOH is converted 
into sodic zincate, Zn(ONa) 2 , which is soluble in water. Filter 
and wash the ppt. The fact that NaOH produces a ppt. 
must not be accepted as final proof of Mn, but a special test 
for it should be made. Touch a heated loop to a little fusion 
mixture composed of equal parts of Na 2 C0 3 and KN0 3 , then 
heat in the blow-pipe flame for an instant to cause the salts 
to adhere to the wire. Touch the salt to the ppt. and fuse 
until bubbles of gas no longer appear. Mn if present will 
give an opaque blue-green bead owing to the formation of 
sodic manganate, Na 2 Mn0 4 . 

Add to the filtrate, which may contain Zn, enough 
H(C 2 H 3 2 ) to render the solution acid. Zn(ONa) 2 will 
change to zincic acetate, Zn(C 2 H 3 2 ) 2 . 

Pass H 2 S through the solution until it smells strongly of the 
gas. Zn if present will appear as a gray-white ppt. of zincic 
sulphide, ZnS. Sometimes the ppt. becomes apparent only 
on long standing. 

Procedure when the Phosphates or Oxalates are Present. — 
At first sight it is not apparent why the presence of phos- 
phates or oxalates should occasion a change in the course of 
analysis; it is due to the fact that they cause certain metals 
properly belonging elsewhere to be ppt. along with the metals 
of group III. 

The ppt. of the metals of group III takes place in an 
alkaline solution. Under these conditions phosphates or 



312 WET METHOD OF ANALYSIS 

oxalates of Ba, Sr, Ca and Mg are also ppt. since they are 
soluble only in an acid solution. Therefore, if a solution 
under examination contains phosphates or oxalates and at 
the same time Ba, Sr, Ca, or Mg, these metals will be ppt. in 
group III along with the regular members of the group and 
the course of analysis must be modified in such a way as to 
admit of their detection in this place. 

Add to a small portion of the filtrate, which has been 
evaporated with cone. HN0 3 , dil. H 2 S0 4 . If no ppt. appears 
after five minutes' standing, Ba and Sr are absent. If there is 
a ppt., filter and wash it thoroughly with hot water. It may 
consist of the sulphates of Ba and Sr. It is best examined 
for Ba and Sr in the spectroscope, the presence of the former 
being recognized by four green bands and the latter by one 
orange, two red, and one blue band. To test for Ca, take 
either the solution found free from Ba and Sr, or the filtrate 
from the ppt., caused by these two metals and add to it three 
times its volume of alcohol; CaS0 4 , being less soluble in a 
mixture of alcohol and water than it is in water, will ppt. if 
Ca is present. To confirm the presence of Ca filter and dis- 
solve the ppt. in a little hot water. 

The addition of a solution of ammonic oxalate, (H 4 N) 2 - 
C 2 4 , will produce a white ppt. of calcic oxalate, CaC 2 04. 
Having completed the test for Ba, Sr and Ca, return to the 
main portion of the filtrate which was evaporated with cone. 
HNO3. Nearly neutralize the free acid with dry Na 2 C0 3 , 
taking care to have no permanent ppt. 

Then add to it solution of ferric chloride, FeCl 3 , until a 
drop of the solution placed upon a watch-glass gives a yellow 
ppt. when made alkaline with a drop of (H 4 N)OH. FeCl 3 
is added because Fe will combine with H 3 P0 4 and H 2 C 2 4 
and thus prevent the alkali earth metal from being ppt. as 
phosphates and oxalates at the next step in the analysis. Add 
to the solution 25 c.c. of BaC0 3 suspended in water, stir 
occasionally and let stand ten minutes. It will be well to con- 
sider what metals will be ppt. at this point, and what remains 
in solution. The ppt. produced by BaC0 3 is not essentially 
different from the ppt. produced by the same reagent when 



ANALYTICAL PROCEDURE 313 

the phosphates and oxalates are absent. It may contain Al, 
as Al(OH) 3 and Cr as Cr(OH) 3 ; it must contain Fe combined 
with H3PO4 or H2C2O4 and the excess of BaC0 3 . Examine 
it precisely as before and test the original solution for Fe, 
remembering a ppt. appearing at this point means nothing, 
since FeCl 3 was added above as a reagent. The filtrate from 
the BaC0 3 ppt. may contain Mn, Zn, Sr, Ca, and Mg; it 
must contain Ba. Heat on the iron plate nearly to boiling 
and add dil. H 2 S0 4 until a drop ceases to cause a ppt. Ba and 
Sr will be ppt. Filter, make the filtrate alkaline with (H 4 N)OH 
and add (H 4 N) 2 S. If there is no ppt. Mn and Zn are absent. 
A ppt. means Mn and Zn, one or both. Filter and wash the 
ppt, with hot water. Then dissolve it in cold dil. HC1. 
Render the solution alkaline with NaOH and heat nearly 
to boiling on the iron plate. If there is no ppt., Mn is absent. 
If there is a ppt., filter, wash and examine as before for Mn 
with Na 2 C0 3 and KN0 3 bead. The filtrate from the ppt. 
which may contain Mn is acidified with H(C 2 H 3 2 ) and then 
saturated with H 2 S. Zn if present will be ppt. as gray-white 
ZnS. The filtrate from the ppt. caused by (H 4 N) 2 S or the 
solution found not to contain Mn or Zn is treated with 
ammonic oxalate, (H 4 N)C 2 4 . A white ppt. is CaC 2 4 due to 
the presence of Ca; filter and add sodic phosphate, Na 2 HP0 4 , 
to the filtrate. If Mg is present it will be ppt. as white crys- 
talline ammonic magnesic phosphate, Mg(H 4 N)P0 4 . 

Group IV. 

Introductory. — Four metals are included under this heading, 
viz.: (1) Barium, Ba; (2) Strontium, Sr; (3) Calcium, Ca; 
(4) Magnesium, Mg. With the exception of Mg these metals 
are alike in their behavior toward ammonic carbonate, 
(H 4 N) 2 C0 3 , as they are ppt. by this reagent from a neutral 
or alkaline solution. Under these conditions Mg is not ppt. 
at all but the other members of the group form carbonates, 
viz. : 

1. Ba appears as white baric carbonate, BaC0 3 . 

2. Sr appears as white strontic carbonate, SrC0 3 . 



314 WET METHOD OF ANALYSIS 

3. Ca appears as white calcic carbonate, CaC0 3 . 

4. Mg remains in solution. 

They may be identified by characteristic tests: 

1. Ba by insoluble white, BaS0 4 , appearing immediately. 

2. Sr by insoluble white, SrS0 4 , appearing tardily. 

3. Ca by insoluble white, CaC 2 4 . 

4. Mg by insoluble white crystalline, Mg(H 4 N)P0 4 . 
Analytical Procedure. — Add to the filtrate from the (H 4 N) 2 S 

ppt. of group III, or to a solution free from the metals of 
groups I, II, III, 10 c.c. of (H 4 N)C1, provided this reagent is 
not already present. 

Note. — After the addition of (H 4 N)C1 the solution is 
made alkaline with (H 4 N)OH. If the solution contains Mg 
and (H 4 N)C1 is not present the addition of (H 4 N)OH will 
cause the partial ppt. of Mg as Mg(OH) 2 and this metal may 
escape detection. Soluble compounds of Mg form double 
salts with (H 4 N)C1 and upon them (H 4 N)OH has no action. 
It is for this reason that (H 4 N)C1 is used at this point as 
well as in group III. If the solution is not alkaline, make it 
so by adding a slight excess of (H 4 N)OH. Heat nearly to 
boiling on the iron plate and add ammonic carbonate, 
(H 4 N) 2 C0 3 , until a drop ceases to cause a ppt. 

If you are dealing with a much diluted filtrate from group 
III, it may be advisable to concentrate it by evaporation 
before making this precipitation. When ppt. is complete, 
set aside for a few minutes and then filter. The filtrate may 
contain Mg together with the members of group V. Add to a 
small portion of the filtrate a few drops of a solution of sodic 
phosphate, Na 2 HP0 4 . If Mg is present an insoluble white 
crystalline ppt. of ammonic magnesic phosphate, (H 4 N)- 
MgP0 4 will appear. If the quantity of Mg is small it may 
be necessary to let the solution stand for some time. The 
precipitate should be examined with a lens to make sure that 
it is crystalline because, in case of incomplete ppt. by (H 4 N) 2 - 
C0 3 , some Ba, Sr, or Ca might pass into this filtrate. 
Na 2 HP0 4 ppt. these metals also from solution but the com- 
pounds are amorphous. Having tested for Mg, keep the 
remainder of the filtrate for the group V tests. The pre- 



ANALYTICAL PROCEDURE 315 

cipitate, which may consist of BaC0 3 , SrC0 3 and CaC0 3 , 
is first thoroughly washed with hot water. It is then dis- 
solved on the paper with acetic acid, H(C 2 H 3 2 ). The car- 
bonates are decomposed and converted into acetates. To a 
small portion of the solution add a few drops of solution 
CaS0 4 . Three cases may arise, viz.: (1) A white ppt. may 
appear immediately. It will be BaS0 4 , and Ba is present. 
Sr and Ca also may be present. (2) A white ppt. may appear 
tardily. It will be SrS0 4 , and Sr is present. Ba must be 
absent but Ca also may be present. (3) There may be no 
ppt. at all. Then Ba and Sr are absent, Ca alone is present 
and the original ppt. is CaC0 3 . 

The subsequent course of analysis depends upon the case 
which arises and it must be modified accordingly. If Ba is 
present it must be removed from solution before testing for 
Sr and Ca can be made. Add solution of potassic chromate, 
K 2 Cr0 4 , in slight excess to the remainder of the H(C 2 H 3 2 ) 
solution. Ba will be ppt. as Ba chromate, BaCr0 4 , but Sr 
and Ca will remain in solution. Filter and make the filtrate 
alkaline with (H 4 X)OH. A sufficiency of the reagent will 
change the color from red to yellow. Heat nearly to boiling 
on the iron plate and as before add (H 4 X) 2 C0 3 until a drop 
ceases to cause a precipitate. If there is no ppt., Sr and Ca 
are absent and the original ppt. must have consisted of BaC0 3 
alone. If a ppt. appears, filter after a few minutes' standing 
and reject the filtrate. The ppt. which may consist of SrC0 3 
and CaC0 3 , one or both, must be washed with hot water until 
all traces of yellow color is removed. It is then dissolved 
on the paper in H(C 2 H 3 2 ). Again the carbonates have been 
converted into acetates. Add a few drops of solution of 
CaS0 4 to a small portion of the acetate solution. Two cases 
may arise, viz. : (1) A white ppt. may appear tardily. It 
would beSrS0 4 , and Sr is present; Ca may also be present. 
(2) There may be no ppt. at all. Then Sr is absent and the 
precipitate caused the second time by (H 4 X) 2 C0 3 must have 
consisted of CaC0 3 alone. If Sr is present it must be 
removed before testing for Ca. Add dil. H 2 S0 4 in slight 
excess to the remainder of the H(C 2 H 3 2 ) solution, from 



316 WET METHOD OF ANALYSIS 

which Ba has been removed or in which Ba was originally 
found absent. 

Note.— Observe that in case Ba is shown to be absent 
when the test is made with CaS0 4 in the first H(C 2 H 3 2 ) 
solution of the carbonates, and Sr is present, the analysis 
continues from the paragraph beginning "If Sr is present, 
etc." 

If Sr is also shown to be absent, then it continues from the 
paragraph below beginning, "If Sr is absent, etc." 

As SrS0 4 separates slowly, do not proceed hastily, but 
allow the solution to stand about fifteen minutes. If Ca is 
present in large quantity, or the solution is concentrated, 
some CaS0 4 will also be ppt. with SrS0 4 , but this may be 
disregarded. 

Filter and make the filtrate alkaline with (H 4 N)OH. Then 
add solution of ammonic oxalate, (H 4 N) 2 C 2 4 . If Ca is 
present, a white ppt. of calcic oxalate, CaC 2 4 , will appear. 
If Sr is absent whether Ba was originally absent or was 
removed (H 4 N)OH and (H 4 N) 2 C 2 4 added to the rest of the 
H(C 2 H 3 2 ) solution precipitates CaC 2 4 , if Ca is present. 

Gkoup V. 

Introductory. — Four metals are included under this heading, 
viz.: (1) Ammonium, (H 4 N); (2) Sodium, Na; (3) Potassium, 
K; (4) Lithium, Li. These metals differ from those of the 
preceding groups in having no general reagent which can be 
used to precipitate them from solution. This is because their 
compounds with few exceptions are readily soluble in water. 
Therefore they remain in solution after the other metals 
have been precipitated and tests have to be used by which 
each can be detected in presence of the others. Ammonium, 
(H 4 N) — this substance is hypothetical and exists only in 
combination with other elements. It is placed in this group 
because its compound closely resembles in properties those 
of the alkali metals. In testing for it, it is necessary to show 
that ammonic, H 3 N, can be obtained from the solution, 
or a substance under examination. In the case of a solution 



AMMONIUM TEST 317 

which has passed through the course of basic analysis a test 
for ammonium evidently cannot be made at the end of the 
analysis, because ammonium salts have several times been 
used as reagents and they must be in the solution. Some 
of the original material must always be used in testing for 
this substance. 

Ammonium Test. — Select a tall beaker and have it clean. 
Place some dry calcic hydroxide, Ca(OH) 2 , in the bottom, 
but do not get it on the sides. Add a little of the original 
solution or solid dissolved in water and H 3 N will be set 
free if salts of (H 4 N) are present. Often H 3 N may be 
detected by its odor, but it is better to place a piece of 
moistened turmeric paper on the outside of a clean dish and 
set it on the beaker if a test for (H 4 N) is not obtained in 
the cold; warm gently on the iron plate. Avoid spattering, 
since Ca(OH) 2 also has the same effect upom turmeric paper. 

Tests for the three remaining members of this group must 
be made with the filtrate of group IV. Owing to the fact that 
this filtrate may contain Mg also, two cases arise, viz.: 

1. When Mg has been shown to be present, Mg must be 
removed from solution before the remaining test of this group 
can be made. Pour the solution into a dish and evaporate 
under the hood over wire gauze to complete dryness, and 
continue the heating until all fuming has ceased. To insure 
good results directions must be followed carefully. The 
object of this step is the complete removal of (H 4 N) salts, 
as they interfere with the removal of Mg. When heat 
expels nothing more, allow the dish to cool and dissolve the 
residue in 5 c.c. of water. Add 5 c.c. of solution of baric 
hydroxide, Ba(OH) 2 , or enough to give an alkaline reaction. 
Mg will be completely precipitated as magnesic hydroxide, 
Mg(OH) 2 . Filter and heat the filtrate on the iron plate 
nearly to boiling. The excess of Ba(OH) 2 must now be 
removed. Add dil. H 2 S0 4 until a drop ceases to cause a ppt. 
and filter. Again evaporate the filtrate under the hood and 
heat until everything volatile has been expelled, cool and 
dissolve the residue in 5 c.c. of water. Na, K and Li if present 
will now be in solution as NaHS0 4 , KHS0 4 and LiHS0 4 ; 



318 WET METHOD OF ANALYSIS 

the acid sulphate and this solution after being filtered into 
a clean specimen tube may be used for the flame test to be 
described later. 

2. When Mg has been shown to be absent, as already 
described, the filtrate from group IV must be evaporated 
until fuming has entirely ceased. The cooled residue is 
dissolved in 5 c.c. of water, and the solution filtered into a 
clean specimen tube for use in the flame tests. 

In the absence of a spectroscope the flame tests may be 
observed through one or more pieces of cobalt glass. Dip 
a platinum wire into the filtrate from the specimen tube and 
hold wire in the colorless flame of a Bunsen burner. 

The Na light is absorbed by passing through the cobalt 
glass and the flame will thus appear colorless. In viewing 
the sodium flame without the use of the cobalt glass it has 
a yellow color. The potassium flame appears violet, and 
through the cobalt glass more of a crimson; in this way Na 
and K may both be detected. However, Li appears crimson 
in the flame and also crimson through the cobalt glass, 
resembling the K flame. Li and K cannot be distinguished 
from each other by using the cobalt glass. In this case it 
will be necessary to use a spectroscope. 



CHAPTER XXVII. 
ELECTROMETALLURGY. 

When an electric current is passed through a solution of 
a salt of a metal, decomposition takes place and the metal 
is precipitated from solution. Depending upon the conditions 
under which the metal has been precipitated, it may be 
obtained in powder form or as a coherent mass. 

The process of so precipitating metals is called electro- 
metallurgy. 

There are two different methods in use in electrometallurgy. 

1. The metal is deposited in a mold until a desired thick- 
ness has been obtained. This process is known as electro- 
typing or galvanoplactics. 

2. Depositing the metal upon a metallic surface as a thin, 
coherent coating. This process is known as electroplating. 

ELECTROTYPING. 

In this process a mold is first prepared. This process has 
been used in dentistry for the construction of a gold base for 
the attachment of artificial teeth. This process has not 
proved successful in dentistry; however, it will serve to illus- 
trate this method of depositing metals with an electric 
current. 

The plaster model is carefully prepared and thoroughly 
dried, it is then boiled in paraffin so as to make it impervious 
to the solution of the bath. The surfaces to receive the metal- 
lic deposit is then coated with a thin layer of graphite, care 
being taken not to efface the fine lines of the model. Graphite 
is used so as to form a conducting surface upon the model. 
The model is then connected in metallic circuit with the 



320 ELECTROMETALLURGY 

negative pole of a battery, the positive pole is connected with 
a strip of metal having at least the same surface area as the 
model. If the metal to be deposited is gold, then a sheet of 
gold having at least the same area as the model should be 
used. 

The bath is composed of a nearly neutral solution of gold 
chloride in potassium cyanide. The nature of the gold 
deposited is dependent upon the density of the current; with 
a current of moderate density the gold will be deposited as a 
crystalline mass but with a greater density of the current 
it will be thrown down as a non-coherent mass. 

As the current passes from the positive electrode (gold 
sheet) the charge is conveyed by the gold ions in the solution 
to the negative electrode (the model), the gold ions here 
lose the electrical charge and the gold is deposited upon the 
model. While this change is taking place the cyanogen 
ions, which possess a negative charge, are passing in an 
opposite direction and upon coming in contact with the 
anode (gold sheet) lose their charge and attack the gold, 
in this manner the bath is kept of a constant concentration 
as to the gold which is in solution. In the case which is 
illustrated the gold piece of the anode should exceed in weight 
the metallic base which is desired. 

ELECTROPLATING. ELECTRO GILDING./ 

In order to deposit a thin film of gold upon the surface 
of a metal a preliminary preparation of the surface is neces- 
sary: (1) The object must be freed from any fatty material. 
This may be accomplished either by heating and then 
removing any oxides which may be found by the use of 
dilute nitric acid, finally washing thoroughly with distilled 
water. In this operation the piece should not come in contact 
with the hands of the operator or the piece will be con- 
taminated by the grease from the hands. (2) The piece may 
be heated in a solution of sodium carbonate and in this way 
remove the grease. After this treatment a thorough washing 
is necessary to remove an adhering sodium carbonate solution. 



ELECTROPLATING— ELECT ROGILDING 321 

After the piece has been freed from grease its surface should 
be thoroughly brushed with a hard brush, washed in distilled 
water and dried in gently heated • sawdust. Connect the 
piece with the negative pole from a battery and have a piece 
of gold of at least the same surface area as the piece to be 
plated. 

The gold bath may be prepared by having one part auric 
chloride, (AuCl 3 ), ten parts potassium cyanide and two 
hundred parts distilled water. The density of the current 
should not exceed 0.8 ampere per square decimeter of the 
surface of the piece to be plated. 

Silver, copper, and German silver may be gilded, while 
iron, steel, zinc, tin and lead are very difficult to plate. Some 
metals take a much better plating if they are first copper 
plated. The color of the gold plating may be attained by 
adding small quantities of silver or copper to the bath. 

Electrosilvering. — This process may be carried out in the 
same manner as the above except the anode must be of 
silver and also a silver bath must be used. 

Silver Bath. 

Silver cyanide 2 parts 

Potassium cyanide 2 parts 

Water 250 parts 

The density of the current should be 0.33 ampere per 
square decimeter of the surface of the kathode. 

Nickel Plating. — The following is said to produce a good 
nickel plating: 

Preparation of Bath. — Dissolve one part of nickel ammo- 
nium sulphate in ten parts by weight of water. The nickel 
ammonium sulphate should be free from alkaline oxide and 
other impurities. After the solution is prepared, filter. The 
anode should be of nickel, using the same size electrode as 
specified above under Gold Plating. One difficulty in nickel 
plating is that the metal is not always uniformly deposited 
and may scale from the piece. To overcome this difficulty 
the object should be removed from the bath frequently and 
21 



322 ELECTROMETALLURGY 

polished, then replace until a sufficiently heavy plating of 
nickel is obtained. 

Platinum plating is effected by dissolving platinum 
hydrate in syrupy phosphoric acid and this solution diluted 
with water until it contains 1.2 to 1.5 per cent, of the hydrate. 
The anode is either of carbon or platinum and the strength 
of the bath is kept constant by the addition of the hydrate. 

Objects of iron, nickel and zinc must first be copper plated 
before they can receive a deposit of gold, silver or platinum. 

Contact Process. — In this process a strip or rod of an electro- 
positive metal is brought in contact with the object to be 
plated when the latter is immersed in a bath containing a 
salt of the metal to be deposited; for example, a plate of zinc 
in a bath of gold cyanide. When the zinc touches the object 
a battery is formed, zinc being the anode and the object the 
kathode, and the gold cyanide the electrolyte; the solution 
is decomposed and gold is deposited upon the object. 



INDEX 



A 



Acid oxide, 36 
Alchemy, 18 
Alloys, 64 

annealing of, 72 

chemical compounds in, 66, 70 

color of, 69 

composition of, 70 

decomposition of, 71 

denned, 64 

density of, 68 

ductility of, 69 

eutectics in, 66 

fusibility of, 75 

hardness of, 67 

influence of constituent metals 
in, 76 

kinetic theory on, 64 

liquation of, 72 

malleability of, 69 
of base metals, 74 
of noble metals, 74 

Mattheisson's theory on, 64 

microscopic examination of, 101 

mixed metals in, 65 

preparation of, 74 

study of, 100 

table of, 70 

temper in, 73 

tenacity of, 69 

thermic analysis of, 100 
Aluminum, 235 

action of acids on, 240 
of caustic potash on, 241 

alloys of, 241 

annealing of, 73, 243 

artificial denture made from, 238 

atomic weight of, 243 

bronze, 154 



Aluminum, bronze, solder for, 
154 

casting of, 237 

color of, 237 

heat conductivity of, 243 

melting-point of, 243 

method of melting, 238 

occurrence of, 253 

ores of, 235 

oxidation of, 237 

properties of, 237 

reduction of, 235 

soldering of, 239 

specific gravity of, 243 
Amalgam, 270 

aging of, 276 

alloys, balanced, 277 
dental, 274 

amalgamation, direct, 271 
indirect, 272 

ammonium, 127 

behavior of mercury in, 271 

binary, 286 

classification of, 272 

copper, 153, 289 

defined, 126 

discoloration of, 247, 274 

edge strength of, 275 

flow of, 275 

gold, 289 

other metals in, 290 

permanency of form, 273 

platinum in, 289 

quantity of mercury required, 
285 

requirements of, 272 

silver in, 287 

spheroiding, 275 

testing, expansion and contrac- 
tion, 280 



324 



INDEX 



Amalgam, testing, flow and crush- 
ing strength, 282 

physical properties of, 279 

tin, 286 

working properties, 273 

zinc, 273 
Analysis, dry methods of, 24, 291 
bead tests, 291 
bulb tube tests, 292 
charcoal tests, 292 
flame tests, 291 
fusion tests, 291 
systematic blow-pipe tests, 
295 

gravimetric, 25 

volumetric, 25 

wet methods of, 24, 298 
Anglesite, 115 
Annealing defined, 72 

of base metals, 73 

of noble metals, 73 
Antifriction metal, 160 
Antimony, 157 

action of acids upon, 159 

amorphous, 158 

antifriction metal, 160 

Britannia metal, 160 

compounds of, 158 

conductivity of heat of, 158 

impurities in, 158 

properties of, 158 
magnetic, 158 

purification of, 158 

reduction of, 157 

tartar emetic, 157 

type metal, 160 

uses of, 160 
Apparatus, crucibles, 88 

scorifiers, 89 
Argentite, 128 
Assaying defined, 25 

of gold and silver, 196 
Atomic weight, 20 

volume, 62 
Austentite, 74 
Autogenous soldering, 104 

welding, 61 
Azurite, 146 

B 

Babbit metal, 71 
Balance, 94 



Ball mill, 25 
Base defined, 40 

metal alloys, 75 

metals, 23, 40 
Basic oxides, 28 
Bauxite, 235 
Bean's, Dr., alloy, 165 
Bell metal, 250 
Beryllium, 269 
Bismuth, 143 

alloys of, 145 

compounds of, 144 

detection of, 303 

effects of, on metals, 144 

impurities in, 144 

Lichtenberg's alloy, 145 

nitrate of, 145 

occurrence of, 143 

oxides of, 145 

properties of, 144 

reduction of, 144 

Rose's metal, 145 

solubilities of, 145 

uses of, 144 

Wood's metal, 145, 156 
Bismuthinite, 143 
Blow-pipe, alcohol, 79 

gas, 79 

gasoline, 79 
Boiling points, 29 
Brass, 71, 154 
Britannia metal, 160 
Bronze, 17, 18, 154 
Bunsen burner, 79 



Cadmium, 155 
detection of, 303 
distillation of, 156 
occurrence of, 155 
ores of, 155 
precipitation of, 156 
properties of, 155 
reduction of, 155 
solubilities of, 156 
uses of, 156 

Calamine, 244 

Calcination, 26 

Calomel, 124 

Calorie, 77 



INDEX 



325 



Calx, 11 

Carat, 188 
Carbon, carbide, 73 

temper, 73 
Carborundum, 235 
Cassiterite, 161 
Castner's process, 263 
Catalytic agent, 152 
Cemetite, 74 
Cerussite, 145 
Cinnabar, 122 
Claverite, 169 
Coal gas, 77 

Coefficient of expansion, 32 
Colloidal silver, 136 
Colloids, 47 

Conductivity of electricity, 34 
determination of, 99 

of heat, 31 

determination of, 96 
Copper, 147 

action of acids upon, 151 

amalgam of, 153 

atomic weight of, 147 

blistered, 149 

color of, 150 

compounds of, 152 

conductivity of, 154 

crystallization of, 150 

detection of, 303 

ductility of, 154 

effect of impurities in, 150 

electrolysis of, 150 

gold and, 154, 186 

malleability of, 154 

native, 147 

occurrence of, 147 

ores of, 147 

precipitation of, 151 

properties of, 150 

pure, method of obtaining, 150 

reduction of, 147 

refining of, 147 
wet process, 152 

regulus of, 148 

specific gravity of, 154 

steel, 232 

valency of, 152 
Crouse's alloy, 156 
Corrosive sublimate, 124 
Corundum, 235 
Cowles's process, 236 



Crucibles, 88 
Crushers, 25 
Cryolite, 235 
Crystallization, 53 
Cupels, 90 



Dental alloy, 71 
Desiccation, 27 
Desilverization process, 130 
Determination of temperature, 93 
Deville and Debray's process, 202 
Distillation, 26 
Dorrance alloy, 71, 189 
Draw-plate, 92 
Dross, 75 
Ductility, 48 

list of, 50 
Dutch brass (Tombac), 154 
Dynamometer, 283 



E 



Elasticity, 58 
Electric welding, 62 
Electrical conductivity, 34, 58 
Electrolysis, 41, 114 
Electrometallurgy, 319 
Electromotive series, 39 
Elements, classification of, 20 
English brass, 154 
Eutectics, 66 
Expansion, 96 



F 



Faraday's law, 41 
Feldspar, 106 
Ferrite, 74 
Ferromanganese, 224 
Flame, oxidizing, 79 

reducing, 79 
Fletcher's, Dr., alloy, 166 
Flotation, 62 
Flux, 27, 75 
Forging, 77 
Fuel, 77 
Furnaces, blast, 79 



326 



INDEX 



Furnaces, chimney draught, 79 

coal, 77 

electric, 87 

Fletcher, 84 

Hoskins's, 87 

muffle, 86 
Fusibility, 28 
Fusing points of metals, 28 



Galenite, 115 
Gangue, 24 
Garnierite, 256 
Gauge-plate, 92 
German silver, 70 
Gold, 168 

action of acids upon, 168 

alloys of, 185 

assay of, 196 

beating of, 182 

brittle, 179, 182 

chemically pure, 179 

agents for precipitating, 179 

clasp, 190 

coin, 70, 189 

compounds of, 195 

conductivity of, 181 

copper and, 186 

corrugated, 182 

cupellation of, 197 

ductility of, 181, 198 

extraction of, 171 

malleability of, 180 

mercury and, 185 

method for changing the carat 
of, 192 

mining of, 171 
hydraulic, 172 
pan washing process, 170 

non-cohesive, 182 

occurrence of, 168 

palladium and, 186 

parting of, 186 

platinum and, 186 

properties of, 180 

purple of Cassius, 194 

reduction of, 176 

amalgamation process, 175 
chlorine process, 175 
cyanide process, 176 



Gold, refining of, 177 

electrolytic process, 176 
nitric acid process, 178 
quartation process, 177 
sulphuric acid process, 178 

scorification of, 197 

silver and, 185 

soft, 182 

solders, 189 

solubilities of, 195 

treatment of scrap, 179 

volatility of, 181, 197 

zinc and, 187 
Greenockite, 155 
Gun metal, 150 



H 



Hall process for aluminum, 236 
Hardness, 52 

density, 53 

determination of, 99 

table of, 100 
Haskell's, Dr., counter-die metal, 

120, 166 
Hematite, 217 

Her6ult process for aluminum, 236 
Horn mercury, 122 

silver, 128 



Ingot mold, 91 

Ionic chemical changes, 39 

Ionization, 37 

Iridium, 211 

properties of, 212 
Iron, 217 

action of acids upon, 222 
atomic weight of, 217 
cast, 223 

classification of, 223 
gray, 224 
malleable, 223 
properties of, 221 
crystallization of, 234 
detection of, 223 
ductility of, 222 
malleability of, 222 



INDEX 



327 



Iron, melting point of, 234 
meteoric, 217 
occurrence of, 217 
ores of, 217 
passive, 222 
properties of, 221 
puddling process for making, 224 
reduction of, 219 

by blast furnace, 219 

by electrothermic process, 221 

by hydrogen, 222 
relation of carbon to, 226 
short, cold, 224 

red, 224 
specific gravity of, 221 
wrought, 224 

fibrous texture of , 224 

percentage of carbon in, 224 

red short, 224 



Kaolin, 106 
Kinetic theory, 64 



Latent heat, 65 
Lead, 65 

action of acids upon, 118 

alloys of, 120 

amalgam of, 119 

atomic weight of, 115 

compounds of, 118 

counter-dies of, 119 

detection of, 299 

occurrence of, 115 

ores of, 115 

oxides of, 118 

properties of, 117 

reduction of, 115 

solid flow of, 117 

specific gravity of, 117 

tenacity of, 117 

uses of, 115 
dental, 119 
Lichtenberg's metal, 156 
Liquation, 72 
Lithium, 267 
Lode stone, 217 
Low fusing alloys, 145 



M 



Magnesium, 268 
Magnetism, 59 

diamagnetic, 60 

paramagnetic, 60 
Malleability, 48 

list of, 49 
Matte, 27 

Matter, composition of, 20 
Matthiesson's theories, 64 
Mellotes metal, 71, 146 
Mercury, action of grease upon, 123 
of iodine upon, 124 

amalgams of, 126 

atomic weight of, 122 

boiling point of, 123 

crystallization of, 123 

compounds of, 124 

melting point of, 123 

occurrence of, 122 

ores of, 122 

properties of, 123 

purification of, 123 

solubilities of, 124 

test for base metals in, 123 

vermilion, 125 
Metamorphic rock, 106 
Metals, agents which volatilizes, 60 

base, 23 

oxides of, 36 

boiling points of, 29 

classification of, 22 

colloidal condition of, 47 

color of, 46 

compounds of, 106 

conductivity of electricity, 34 
of heat, 31 

crystallization of, 53 

defined, 28 

ductility of, 48 

elasticity of, 58 

expansion of, by heat, 32 

fusion-point of, 28 

hardness of, 52 
density of, 53 

identification in their ores, 24 

ions, 37 

luster of, 28 

magnetism of, 59 

malleability of, 48 

native, 23 



328 



INDEX 



Metals, native, crystal forms of, 58 

noble, 22 

occlusion of gases by, 60 

odor and taste of, 44 

opacity of, 60 

potential difference of, 42 

replacing hydrogen of acids, 35 

sonorousness of, 58 

sources of, 23 

specific gravity of, 45 
heat of, 44 

tenacity of, 48 
Metallurgy defined, 20 

history of, 17 

primitive, 18 

relations to chemistry, 20 
Micrometer, 280 
Mineral defined, 23 
Molyneaux's alloy, 156 
Mosaic gold, 250 
Muntz metal, 154 



N 

Nagyagite, 169 

Native gold, analysis of, 169 

Newton's alloy, 71 

Niccolite, 254 

Nickel, 254 

action of acids upon, 256 

atomic weight of, 254 

coin, 256 

color of, 255 

detection of, 308 

ductility of, 255 

effect of, on copper, 255 

elasticity of, 257 

electrolytic process of refining, 
255 

electroplating with, 256, 321 

malleability of, 255 

matte, 254 

melting point of, 257 

Mond's process of refining, 254 

occurrence of, 254 

ores of, 254 

oxidation of, 256 

passive condition of, 256 

properties of, 256 

reduction of, 254 

steel, 233 
Noble metals, 74 



Occlusion, 60 
Odor and taste, 44 
Opacity, 60 
Ore denned, 24 

treatment of, 25 
Osmiridium, 211 
Osmium, 211 

properties of, 211 



Palladium, 211 

properties of, 214 
Patera process, 130 
Pattinsen's process, 131 
Percy-Patera process, 134 
Pewter, 71 
Phylogiston, 19 
Platinoid, 71 
Platinum, 199 

alloys of, 207 

compounds of, 206 

ductility of, 203 

gold and, 207 

group, 23 

iridium and, 208 

lead and, 208 

malleability of, 203 

melting scrap, 208 

mercury and, 208 

reduction of, 200 

Deville and Debray's process, 

200 
Wollaston's process, 200 

separation of, 209 

silver and, 207 

solubilities of, 206 

sponge, 204 

substitute for, 204 

tin and, 208 

welding of, 204 
Plumber's solder, 71 
Potassium, 266 

compounds of, 266 

detection of, 316 

occurrence of, 266 

properties of, 266 

reduction of, 266 
Potential difference, 42 



INDEX 



329 



Potential difference, list of, 43 

of dental amalgams, 43 
Producer gas, 77 
Purple of Cassius, 194 
Pyrometers, 94 



Reduction denned, 109 

of chlorides, 111 

of oxides, 113 

of sulphides, 112 
Refractory materials, 88 
Regulus, 27 
Rhodium, 211 

properties of, 213 
Richmond's, Dr. S. M., alloy, 166 
Roasting, 26 

dishes, 90 
Rolling mill, 92 
Rose's alloy, 145 
Ruthenium, 214 



S 



Scorifier molds, 91 
Scorifiers, 89 
Siderite, 217 
Silver, 128 

action of acids upon, 139 

of atmosphere upon, 137 
aUoys of, 139 

dental, 140 

platinum, 140 

von Eckart's, 141 
coin, 70, 140 
colloidal, 136 
compounds of, 138 

chloride, 138 

cyanide, 136 

oxide, 138 

nitrate, 138 

sulphate, 139 
detection of, 300 
gold and, 140 
occlusion of, 137 
occurrence of, 128 
properties of, 136 
pure, 134 
reduction of, 128 

amalgamation process, 129 



Silver, reduction of, Patera pro- 
cess, 130 
Pattinson's process, 131 
Ziervogel's process, 131 

solder for, 141 

spitting of, 137 
Slag, 26 
Smelting, 26 
Smithsonite, 244 
Sodium, 244 

compounds of, 264 

detection of, 316 

occurrence of, 263 

properties of, 264 

reduction of, 263 
Soldering, 101 

autogenous, 104 

requirements for, 102 
Solders, composition of, 166 

flux for, 166 

soft, 166 
Solid flow, 62 
Sonorousness, 58 
Specific gravity, 45, 93 

heat, 45 

determination of, 97 
Sphalerite, 244 
Spiegeleisen, 224, 229 
Steel, 226 

acid, Bessemer process, 230 

action of carbon on, 230 

aluminum, 232 

basic, Bessemer process, 230 

Bessemer process, 229 

case hardening, 231 

cementation process, 229 

chrome, 232 

copper, 232 

crucible process, 228 

electrothermic process, 229 

ferromanganese, 224, 229 

hardening, 230 

Harveyized, 232 

high-speed, 234 

letting down, 231 

manganese, 233 

nickel, 232 

properties of, 232 

tungsten, 233 

vanadium, 234 
Sublimation, 26 
Swaging, 62 



330 



INDEX 



Tantalum, 258 

occurrence of, 258 

solubilities of, 258 

uses of, 259 
Tempering, 73, 230 
Tenacity, 48, 52 

determination of, 100 
Thermite welding, 62 
Tin, 161 

action of acids upon, 163 

alloys of, 165 

atomic weight of, 161 

block, 165 

compounds of, 162 

cry of, 162 

detection of, 306 

foil, 164 

gold and, 164 

gray, 162 

impurities in, 167 

melting point of, 167 

occurrence of, 161 

ores of, 161 

oxidation of, 162 

poushing putty, 163 

properties of, 162 

reduction of, 161 

solvents for, 163 

specific gravity of, 167 

uses of, 164 
Troostite, 74 
Type metal, 70 



Vermilion, 124 
tests for, 125 
Von Eckart's alloy, 125 



W 

Wedelstaedt test-tube, 279 
Weights, assay, 196 
Welding, 61, 104 

autogenous, 61 

fusion, 61 

electric, 62 

Goldschmidt's process, 62 

Thermite, 62 
Wollaston's process, 200 
Wood's alloy, 145 



Ziervogel process, 134 
Zinc, 244 

action of caustic alkalies on, 
248 

of dilute acids on, 249 

of hydrochloric acid on, 249 

of nitric acid on, 249 
alloys of, 249 
amalgam of, 249 
atomic weight of, 244 
best temperature for working, 

247 
blende, 247 
boiling point of, 247 
compounds of, 251 
counter-dies of, 251 
detection of, 311 
occurrence of, 244 
properties of, 247 
reduction of, 245 
specific gravity of, 247, 253 
volatility of, 247 
Zincite, 244 



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